@VEGASPascal Here's a simpler solution. If we can right click and "Surround Event with Envelops", that would speed up the process and accomplish the desired effect.
So essentially, VEGAS would surround the beginning and end of the event with envelops in which the points are drawn automatically. Then we choose the composite mode of the track. So all you're doing is leveraging an existing mechanism, but making it faster instead of asking us to draw points ourselves.
Though that still does leave us with the inability of having multiple blending modes on the same video track, which means we need more video tracks - but hey, I'll take what I can get
This already exists in Vegas. I use it all the time to duck my audio. Just do a loop region of your event (double-click on it will do) then simply drag down the envelope, point will be auto-created at the beginning and end of the loop region. In the image below, the envelope points were created automatically as I dragged down the compositing envelope. It will work with any envelope.
You can even adjust how the points are auto-created using "Time selection envelope fade (ms)" in Pref/Editing