Yes, the MEM switch is no problem, but with your 'full restart' you seem to be right.
I've now tried to load Morphy manually (via the Tab menu) in MessChess, but not even this works, because also the plugin is restarted again and this resets everything.
I guess the only (very complicated) way would be to save the current position, quit the GGM+Gruenfeld program completely, load GGM+Morphy and the load the saved position again - not really practicable.
Yes, for the PM10/PM11 modules I've used the following method in CB-Emu:
These are additional (only data!) modules using a special RAM area. When ChessMaster DM is started, the contents of both modules are copied to 2 different free RAM areas, and when the user switches on any of these modules, its RAM area is simply copied to the special area that the ChessMaster DM expects.

A clever trick, but I doubt this would work for the GGM modules, because these are program+data modules, and of course you can't replace the program area while the program is running.

Regards,
Franz