Interesting question. What do you mean by "glassing the hull"? Are you reattaching the grid, or are you repairing a section of hull lay-up?
By the way, the customer service at Catalina is really good. Many people, including myself, have talked with people there, including Gary Douglas, who can give in depth and knowledgeable information. Have you talked to them?
It sounds like you have a big project in front of you. Good luck, and keep us posted.
The pan should be structurally adhered, although, probably not uniformly. Taking out a small flat section to allow for glass over a thru hull would be very different from removing any part of it's structural framework.
Calling Catalina was excellent advice. Interested in more detail on what you need to do.
Can you provide more details? Where exactly is the damage and how extensive is it? Offhand, removing the structural parts of the interior mold or underlying grid isn't a good idea. Boatyards tend to do this repair from the outside and re-fair the hull. Post your issue over on the C34 owner's website as there are lots of very knowledgeable owners who contribute on the site.