Overall, I think there is quite some repetition, and the section could do with some shuffeling of the info. The most important comments that I have are given below, with the quoted parts of your text they apply to.
"One possibility was that she was a noblewoman pretending to be a healer to go unnoticed as she helped wounded soldiers."
Talissa wasn’t pretending to be a healer. She was performing the duties of a healer. If you are suggesting here that “Jeyne Westerling” was pretending to be a woman named “Talisa” so she could go unnoticed in the war-struck westerlands and so prevent getting caught by Stark soldiers on account of her noble blood, that’s simply what you should say
This would actually have some thematic resonance with the novels - in which Jeyne's mother, Sybell Spicer, was in fact a spy for Tywin Lannister and knew the Red Wedding was going to happen. Thus if Talisa was a Lannister spy, it would be more of a case of condensing mother and daughter into a single character.
Sybel was not a spy for Tywin; As far as we know, she did not pass on any information about Robb to him.
Nor did Sybell know about the Red Wedding:
“I have two sons as well,” Lady Westerling reminded him. “Rollam is with me, but Raynald was a knight and went with the rebels to the Twins. If I had known what was to happen there, I would never have allowed that.” There was a hint of reproach in her voice. (AFFC)
Martin directly stated that the storyline with Talisa in Season 2 of the TV series is not simply what happens "off-screen" in the books with Robb and Jeyne Westerling. Martin did not agree with this change.
Is this based on the “but also that's not a...well, I don't know I shouldn't say more about that."” portion of the quote? I can’t say that there’s a definitive indication of Martin not agreeing with the change in this (I’m not saying that there is no proof, I'm saying that the quote you cite as proof might not actually be proof).
Martin revealed that this was not a single decision to change "Jeyne Westerling" to "Talisa from Volantis" - there was actually an intermediary step, when they were calling her "Jeyne from Volantis", with no surname. This is significant because it explains the previously not understood casting information from August 11 2011, when Westeros.org contacted HBO but was told that Chaplin's character was just named "Jeyne" with no surname. On September 16 2011, filming spies reported that Chaplin introduced her character in dialogue as "Talisa". Thus at some point in that single month, as Season 2 was filming, Martin had a specific meeting with Benioff and Weiss at which he urged them that this wasn't really the same character as from the books, so they should outright give her a different name.
I’d move this to above, where you are actually discussing the casting call, and use the following information to explain the name change from Jeyne to Talissa:
In August 2011, HBO told Westeros.org that Chaplin was cast as “Jeyne”.
By September 2011, her name had been changed to “Talissa” ("Lissa [sic] from Volantis")
According to Bryan Cogman (interview thinkprogress June 8 2012 & interview winteriscoming.net April 2013), the character was originally called “Jeyne”, but her name was changed to “Talisa” during production by Benioff and Weiss, after the writing for season 2 had already been officially wrapped up.
The name change has been suggested by Martin, who felt that “Jeyne” was not the name of a Volantene noblewomen (as stated in the introduction paragraph of the page, lacking a source), and because he felt that the character, as Weiss and Benioff had created her, was too different from “Jeyne Westerling” in Martin’s novels. (Your interview quote shows Martin stating that the characters are two different people, but does not cite that this difference was a reason for Martin to suggest the name change, so such a source should be added here as well).
Initially, there was some confusion about Talisa being a foreign noblewoman specifically from Volantis, given that the aristocracy of that city are particularly obsessed with being pureborn descendants of the Valyrians, thus they all look like Targaryens: pale skin, blonde hair, purple eyes. Volantene aristocrats are quite descriminatory about racial/ethnic appearance. Chaplin, in contrast, is half-Chilean, with dark hair and olive skin - leading to the simple question of why they made her from Volantis instead of another Free City such as Myr (whose inhabitants actually match that her physical appearance). Talisa in the books actually does have a somewhat darker toned appearance, chestnut hair and brown eyes, due to her maternal grandmother actually being a foreigner from the Free Cities (which one isn't specified).
Two things here:
The Old Blood, nobles who can prove their unbroken descent from Old Valyria, make up only part of the population of Volantis. As far as I can recall, it has never been stated that there are no nobles living in Volantis who do not belong to the Old Blood.
In addition, although the Old Blood trace their descent to the Valyrians, and the appearance of the Valyrians is a typical one (purple/blue eyes, silver hair, pale skin), it has never been stated that al Volantene-born people have the Valyrian appearance. For example, Qavo Nogarys (customs officer in Selhorys), is nobleborn, but has black hair. Nor can I recall Tyrion remarking upon the Valyrian appearance of people during his time in Selhory and Volantis.
So the conclusion that all Volantene look like Valyrians/Targaryens is more an assumption.
Comparing Talissa’s appearance to Jeyne’s and remarking upon the fact that Jeyne has eastern ancestors might better be moved to the “Volantis” part of the change.
Writer Bryan Cogman was also asked about the change in subsequent interviews. Cogman explained that he was not directly involved in the change or the writing of this storyline, Benioff and Weiss were, and he had no say in it. Cogman did admit, however, that the change from Jeyne to Talisa was made "during production", after the formal writers' room period for Season 2 had officially wrapped (matching up with the casting announcements and on-set reports). The decision to actually show Robb on-screen at all in Season 2 had been made much earlier than that of course, instead of just giving him the season off and then reappearing in Season 3 (if they strickly followed the books - even Martin didn't want to do that). Cogman also provided some vague explanation for why "Talisa" is from Volantis: the writers had just finished reading A Dance With Dragons after it was released in the break between Season 1 and Season 2, and realized that Volantis was going to be a major location that would actually appear on-screen in later TV seasons, so they wanted to start laying groundwork to introduce it.
The bolded part is only about the name change, and would be better suited above (as indicated earlier)
About the italic text, I'm not sure if this is even necessary to mention, as it is neither about the name change, nor the background change, nor the character change itself.
The last section is not Cogman’s “vague explanation”. This is Cogman’s speculation.
The TV writers, realizing that other Free Cities such as Myr may never appear on-screen in the TV series, might simply have decided to drop the story detail about Volantene aristocrats priding themselves on their Valyrian heritage (perhaps making "TV-Volantis" a sort of condensation of book-Volantis and book-Myr, due to limits of adaptation).
You are the one who suggests Myr. I’d say stick to the facts. Cogman suggests that the producers (not writers) decided to use Volantis because it was set to reappear in later seasons. There’s nothing that suggests a condensation of Volantis and Myr from the books.
In parallel, they may have thought it would take too long to explain that House Westerling is a minor Lannister vassal House that switches sides to the Starks, so they changed Jeyne/Talisa to be a foreigner
This is pure speculation.
keeping only the core point that she is a political nobody, and Robb gains nothing by marrying her.
Although I would personally rephrase this to suite the wikipedia-style better (not calling her a political nobody, but rephrasing it to say that she has no political power in the Seven Kingdoms), the point that the end result of marrying her with regards to "the political advantage the marriage gives Robb" is the same can remain, because it is important to point out.
Thus "why Jeyne Westerling was changed to Talisa" is actually posing two separate questions:
This bolded intercepting questing is quite unnecesssary, because the first of the two bullet points that follow is mostly repeating what you have already said. If you condense that precedes this (remove your own speculations about Myr, remove unnecessary comparisons with Yara Greyjoy and Alton Lannister, etc.) the text in the first bullet point is basically what the end result will be..
After the Robb Stark character was killed off during the Red Wedding at the end of Season 3 of the TV series, Benioff and Weiss bluntly admitted in an interview with Entertainment Weekly: Benioff: "In the TV show, we've spent more time focused on Robb than in the books, mainly because we love Richard Madden as an actor." Jeyne from the books was changed to a romance storyline with "Talisa", specifically because Benioff and Weiss wanted to pander Richard Madden, the actor, in his performance as a romantic lead
That’s not what the quoted part said. They say that Robb received more screen time because they loved the actor. Giving him a romantic storyline would not necessarily have required to change Jeyne into Talisa the way they had. (for example, he could have fallen in love with the captive nobleborn daughter of a Lannister lord).
If there never was an abandoned storyline, and what appeared on-screen in the final version is what they always intended, Benioff and Weiss themselves have stated that they invented a romance subplot with Jeyne/Talisa primarily to show off Richard Madden, the actor.
If their original intention was for her to be a Lannister spy, it was purely meant to fuel Madden's performance when the revelation of her betrayal left him heartbroken.
An abandoned storyline is pure speculation, as is the possible result that might have come from that story line.
Thus the change from Jeyne Westerling to Talisa happened, because it was one of the earlier examples of "We reconceived the role to make it worthy of the actor's talents".
The only thing you have cited is that the producers wanted to give Richard Madden more screen time. You’ve cited nothing about them wanting to give Oona Chaplin more screen time, which is what you imply by citing the expansion of Indirma’s screen time as an example.