Change an Instrument deletes all Notes from Trackpattern?!

Hello i have a Project with some Rewire embedded devices. If i try to change them with a VST Plugin. I get faults. I want hold the Pattern Notes for Track, only change Instruments!!! But if i simply select instrument list and add VST i get error. The VST is showed in instrument list then, but it not plays. It plays still the Rewire instrument. If i first delete instrument from List, and add then the VST i can play with keyboard an it give sound, but the patterntrack notes all are gone. Is there a way to change Samples/instruments/Vsts in generally with saving the Patternnotes in Channel? i hope u understand what i mean.

with best regards