RE: changing footstrap positions
There should be no problem with moving your footstraps when the board is wet.
There is enough clearance at the root of the special PT thread to allow any water that might be trapped to escape out of the plastic FS insert holes.
I would suggest however that you carry a bar of soap and use it to lubricate the footstrap screws whenever you are screwing the the FS screws into a new hole that has not previously had a screw installled.
Also, be sure you use either the Tiki Tool or (much better) a good #3 Philiips screwdriver with a hardened and treated tip.
Use of a good tool here will make yourFS screws last virtually forever.
Do not use a cordless "power driver" as this can rotate the screws at a rate that generates too much heat and can cause you to get poor thread engagement and premature failure of the FS insert.
It won't leak, but you cannot tighten the FS screw to it's full torque, which will reduce the "pull out" strength significantly.
Hope this helps,