Depends what you’re trying to do — if you need instant sound switching you can’t depend on the use of program changes since the amount of time that a plugin needs to switch programs is indeterminate and many plugins don’t even respond to PC messages. There’s also an increased risk of a problem since some plugins just don’t handle them well and if you send MIDI notes to them before they’re finished switching, anything can happen (another reason why we prefer the rackspace concept)
That said, with GP4 or GP5, the easiest way to send different program changes when you switch variations is to use a SendProgramChange scriptlet. It’s attached below as is an example gigfile showing how to use it.
SendProgramChange.gpp_internal (1.7 KB)
ProgramChangeDemo.gig (33.5 KB)