I want to hide some background stuff using different areas of the usable shot
@JHendrix - I’ve had “some” success by doubling-up tracks and making masked-offsets. I’ve invested in BORIS MOCHAPRO and part of that is a means to do this by Tracking and Removal tool. It’s magic!
You can use VEGAS motion tracking to motion track a mask that takes a sample from another track (then edge blur the mask to blend it) if the mask is simple and doesn't move a lot and change shape often, then you can keyframe in any shape changes to the mask you need, but for more complex stuff, Mocha is definitely the best option.
Easiest way is to duplicate your track, then, as Frosty is suggesting, use the top layer (and you can do this more than once, if you'd have multiple spots)..... make a positive mask - in your pan/crop window - of a "good" area and manipulate that (either by pan/crop or track motion) good area over a "bad" area on the track below, and you have feathering on that mask available to blend, You can also apply any other effect to the mask to make it brighter, different shade, etc. to make that match as per 'acceptable.' You'd also have keyframes, or you could employ a motion track if you have camera motion to deal with.