[@NecroKnight] The way I'm doing this is that everything will proceed normally with them. The differences that will make changes, large or small, is the addition of characters. Battles that might have been very close might have different outcomes. More advisors might cause different canon character decisions to be made. I'm sorry if this is a deal breaker, but I'm pretty hard line on making your own character. In your interactions with canon characters you can still treat them as NPCs. If you look in the interest check, my second post contains this. 

Also, as to the why not question. I am strongly of the opinion that you and I or anyone who didn't make the character will write them wrong. I'm not a fan of when comic books change writers or when shows change writers. I notice subtle differences in speech patterns and it irks me. I don't really like keeping canon characters as NPCs but I can bear that. Again, sorry if this ruins your ideas about the game.