I want to do this 1) Press some key to stretch selected envelope track to maximum *) Do something, like move, add automation points 2) Press some key to restore this envelope track to previous hieght Is it possible in reaper?

Currently no, but it's a GREAT idea for a FR!

In the meantime you can use this: Costum Action: -Toggle track zoom to maximum height -Scroll view down Maped to < on my keyboard. Just hover the mouse over the track (or the tracks automation lane) and press <. It is a toggle, so you can just hit it again and have the normal track height again. I made me one without "scroll view down" (shift + <) for full zoom tracks, and one with this action (scroll view down) for fullzoom envelope-lane. Combinate this with: "Toggle show all active envelopes on all tracks" or "select item under mouse cursor (which selects the track aswell)" as U like. Works very good.

thanks for your proposal, but this solution is not good for me because almost all of my tracks have more than one automation lane (at least volume and filter cut off). And your solution is good if you use only one automation lane