A very good question....!
1/ Have you already installed the 7mm x 32mm footsrap screws(mid 2009 and later board build date) and wish to change the footstraps,
2/ Is your board older and you are using the 6mm x 28mm footstrap screws?
If using the longer larger diameter (7mm x 32mm) screws, I would suggest putting a 4 mm long spacer
under the head of the screws.
If using the 6 mm x 28mm screws I think you will be OK.
Perhaps I can get Tiesda You to give you a better answer on this.
Hope this helps,