I wanted to do similar thing, it was to turn off the reverb/delay plugin before the next chords comes in to avoid reverb from previous chords messing up in the next chords but i could not do it. I could do it in logic though. i saw a video where EDM producer kSHMR was doing in a Ableton. It is not possible in Cubase. i read somewhere on Steinberg support that turning plugin off is not technically possible. I found it is possible in Logic and Ableton, not sure it is AU or VST difference or other ASIO thing as Martin advised.