(( I dont see why not, unless you have RPed with some chars and you have RPed about your storyline ALOT and more chars have become invlved, then it can be tedious. ))
((Sure, heck RP the change of story into your RP <gets confused and starts chasing his own tail> 
It can add a little mystery. Heck, I've developed Kata's backstory as she's progressed in game, tweaked it here and there, allowed her to reveal things that weren't strictly true from the beginning.
Just think, comics do it ALL the time. ))
*thinks he should start reading more* its always nice to have a clear start and a clear goal though, otherwise you can make such an elborate story that you get confused and lose sight of the actual meaning on the char all together
((hey i have being r/ping for a day, is it ok to change my story? lol))