You should not be worried about too much hot glue as long as there is not that much penetration into the cedar strip. This will occur much less if it is not sandwiched between strip and form. As for getting the forms out, I would not recommend that you attempt to pry the glassed deck off the forms but rather use a heavy bar and knock the forms out from the inside with lateral force. This is more likely to break the hot glue bond than tear cedar away from the inside of the boat. Also prying up on deck, there is a chance of cracking the resin/fiberglass. I have used a lot!!! of hot glue on some of the detailed designs and been able to knock out the forms in a matter of minutes, beginning in cockpit area and working towards the ends.
Rod