It seems you posted some sec. faster -_-
Anyway Mr., you can always make a bat file, so it changes the ext. of big list of files.
1. Open notepad
2. Type: ren *.fpi *.aaa
(Where 'aaa' is your extension)
3. Save As -> renamer.bat
4. Create a folder called 'Renamed Scripts' and place the new file you just created
5. COPY (I SAID COPY, DON'T MOVE THEM, YOU SHOULD ALWAYS COPY THEM) all the FPI scripts you want to that new fodler.
6. Execute the new file you just created.
This will save you some work, but like i said, MAKE BACKUPS OF EVERYTHING YOU'RE GOING TO CHANGE.
EDIT: Fixed some typos -_-
My love is seperated in 2 parts, 1 of them is 3ds Max 7, the other; FPSC.