Rules (5.7.3) say "fixed at the deck 3505 mm plus or minus 13mm". Would this allow for wedging the mast fore and aft up to 13 mm between races depending on conditions?

My view on this is that is met to be a "pre set" shim and is not be changed on a regular basis

I spoke with Larry Christe on this we both agree that changing the shims between races should not be allowed as the " hole" in the deck is not uniform thru out and are not true side to side

Interesting question. It's the measurer call, but my take is this rule sets the J at 11.5 feet with the 1/2 inch for measurement/construction variance not to allow or restrict adjustment. There is no requirement to have the mast blocked at the partners, so I'd have no problem allowing you to adjust your chocks within the 1/2 inch wiggle room.