I have been editing 3 seconds of a video clip, where I have a keyframe for almost every frame within those 3 seconds (so about 90 frames). Each keyframe has a mask that has been slightly adjusted with each frame to wrap around a moving object (which I'll call Object 1). However, I have now realised there is an Object 2 that also moves within this 3 second clip, and I now need to draw a separate mask around Object 2 for those same 90-ish frames. 

The problem here is because I already have the keyframes established for when I was masking around Object 1, I would need to draw a new mask for each frame to wrap around Object 2. As Object 2 is a difficult shape to mask consistently for each frame (because it has curves) what I would like to do is be able to copy and paste this new mask onto each keyframe, but for some reason, it's not obvious how to do that. I can see that you can copy and paste a whole keyframe, but I don't want to do that as it would overwrite the masking I have done for Object 1.

Does anyone know how I can copy and paste an individual mask from one keyframe to another, without having to copy and overwrite the whole keyframe?

I am using Sony Vegas Pro 17 (Build 284), on a Windows 10 PC.

Thanks very much, let me know if you need anymore clarification on anything.