Fit the gasket and have it DET checked by a proffesional.

CR changes of this magnitude will only affect spark advance requirements
and fuelling will be ok.

You can take 2 degrees out of the map by linking the ignition retard pins
on the ecu which isnt ideal but will get you back on track.

ANy loss on ignition retard will be made up with the CR increase.

I doubt it will have an effect anyway as most tuners allow a safety margin.