That's what I mean, it would be so unnecessary to change Jaqen's story-line just to make him the kindly old man. It won't work if he's the one who shows her the house of Black and White because he'll still have to leave as fast as he can and get to Oldtown. I truly don't want them to change him going to Oldtown and 'becoming' Pate. Since the speculation is that he's there to get the book on how to kill dragons, his role in the future books may be pretty big. I wouldn't want some made-up character getting the credit in the show if they rather make Jaqen the Kindly Old man. They'd even have to make up another random FM to impersonate Pate and follow up on Sam's story-line.
I just can't see it in the long run.