Sega Ages Micky and Donald

I'e noticed that Sega Ages Mickey Mouse and Donald Duck is an emulator (I Think...) of Sega Genesis/Megadrive. infact i've extracted from the ISO the rom Of Castle Of Illusion and it works great on the emulator.

So i've tryed to change that rom with another of same filesize but when the Sega Saturn load the new rom it freezes

The other rom "Donald Duck"seems to be splitted in two files but i don't know how to join them.

So i would know if someone can help me to re-insert any other rom (512k bytes) to play another game correctly.

Sorry for my english... ???
This matter has already been discussed many times in this forum, with simmilar Genesis "emulators" :

Phantasy Star Collection:;t=4216

Even more Phantasy Star:;t=4216

Sonic Jam:;t=4481

Or even threads hijacked yet again to the PSC:;t=1132

The big sumup of this is : Those "emulators" are only parcially so, and they don't run games mutch different of the one's they've been hardcoded to run...
And that's too bad, since Sega did an excellent job here, much, much better than with the Dreamcast Smash Pack.