Sometimes I play a midi file and the Cubasis changes the instruments in Giga instead of playing them. Is this patch change info sent to Giga, and if so how do I remove that from Cubasis
Check your MIDI tracks for Program Changes. I've never really gotten the handle on Program Changes and how GSt really uses them so I just remove them and don't have the sort of problems you seem to be dealing with here. You might do this on a copy track and keep the original muted.
Alternatively, if you can tell Cubasis to not transmit program changes then this could work but maybe you're using them elsewhere and need them.