fin interchanging

on my tri-fin (fcs) board: came with a 7.5 carbon center fin and two side bites. can i change the size of the center fin without changing the size of the bites, or do they have to change proportionally to one another? i'm looking to get a larger center fin, but am wondering if i have to get different bites too....thought maybe they would effect one another.
also, will sliding my center fin up/down in the box effect the side bites performance adversely? sorry for my noob questions. i know they can be a bit tedious.
also, will sliding my center fin up/down in the box effect the side bites performance adversely? sorry for my noob questions. i know they can be a bit tedious.
