Render to Instrument - Editing 36 Keys at once?

Hi. I think to render a vst synth as “Instrument” is a good Alternative to bounce / freeze a track.
For example:
Yesterday i use repro 5 in hq mode to do a Pad.
So i play a accord and you know this take a lot of CPU.
Then i render it to a Instrument with 1 step, 3 octaves and long during and tall times.
I want to loop foward-backward the middle Part of the Sound while Pressing a key.
Is it possible to do it One Times and not 36 Times for every single waveform / key?