Most sailors would not add new holes/inserts, as a bad job might leak. However, if you have a good board repair person nearby, or are good at epoxy, gravity, and routing, you can do it yourself now. Bear in mind, footstrap mounts farther inboard would be set at the flat deck of the board, so you can't effectively lean out and weight the rail, to hold the big sails. It's placement would wreck havoc on your ankles.
A mast track farther back than standard, boom lower than normal, will help the fin raise the windward rail so you can use the existing strap positions with smaller fins.
Conventional thought is that for Formula boards, a fin longer than 58 is needed, if you're going to use the straps in the sub 12 mph range of windspeeds.