Is there some sort of macro facility for inserting repeated actions?
You want to transition from 2 video feeds in one video to full screen video and back?
(Took me a while, I thought you were talking about the viewers on your monitor while editing multicam)

You can do it one time and cmd+C it. Then where you want to use it again do Shift+Cmd+V and choose which effects (in this case transform) you would like to paste. Works for other effects too. 

You can also use a generator that does it, if you can find one or modify or create one in Motion 5 for a more permanent solution. But you'd need to learn how to do that first. 

I know it can be tedious work. With Keyframes, I start with the end and work myself backwards. So when you start out with 2 feeds side by side, keyframe them at the begin situation, go to the frame where you want it all to be one video, that's the end situation. There you adjust it to what it should look like. 
Play it through and if not perfect yet, walk backwards with a few frames at a time (arrow key) to adjust what you need to. 

If the transformations and crops are the same for multiple cuts, you can also screenshot the inspector values for them and just type those in for the next cut.. so you don't need to do it by eyes anymore. 

Hope it helps.. good luck!