I would also love to know how and if you can change presets on an external plug-in. Say for instance, using Native instruments Absynth, and changing the presest to different sounds via a midi controller.
This would solve having to exit peform mode and opening up the plug in and then changing the preset within it.
The first answer is no (a thing apple forget...) but It can be done with some time to setup things.
Can you send your concert (or patch) or try to explain what you really wanna do (which AU...)
If you send me the concert I will try to configure it to you.
Hope I´ve helped.
(moodysenor the same applies to you)