Functional Area effect and how to include old posts?

Dear Experts

Our company is life since Jan 2015.

now, it's required to extract P&L by cost of sales "groups of specific cost centers", so I'm going to define and assign functional areas to design P&L using report painter. my questions are:

1- does activating and assigning functional areas to cost centers affect any other thing ?

2- how to include the old posting in the functional areas? are there any program to run?

Thanks a lot.