Steve, once you output a show, everything is baked in. Blanking is no different. You now have a black bar on the top and bottom of your final output.
If you want to do more work on the show, or change the frame size further, you would go back into the original project, with all the original media attached…like you had never output it in the first place, turn off the blanking, do your tweaks, turn on any new blanking you wanted, and do a new output. That new output would now be baked in.
The term destructive and non-destructive usually refer to you continuing to work in the project, and whether or not corrections, or moves or what ever you have done during your process can be undone. Once you output, you are done.
If you want more than 1 formatted version, you do that all from your master project.
If you reimport your output file, and try to work on it, and tweak it, then you have lost some of your resolution, and any further changes you do could quite easily take it down even further in quality, depending on what you are doing.
Your other option is to output a full screen master and then use that for any future pan and scan versions….including a 2:35 version, or something similar.
Glenn