If you have the FoilMount Version 1.0 then you DO NOT have an access channel to get the T-nuts in and out of the slots in the plate.  If you want to either replace the T-nuts that are in there or exchange the T-nuts between boards than you will need to cut a slot in the plate to achieve this or do it before you stick the FoilMount down.  The above video will walk you through cutting this notch in the plate tracks to allow the T-nuts to be removed or replaced.