Thank you! I had typed "What If" in the Search Topics, Help, and on intuit.com, and struck out. I had not typed it in Search while in Forms Mode (since it is not an IRS Form, but would be more of a Turbotax feature - so it hadn't occurred to me to try that). I will experiment with this What-If tool! Wish Ttax had mentioned its existence somewhere!
I have used Ttax for 30+ years (Mac version) and am probably in Forms Mode more than Interview Mode. The Interview Mode gets frustrating/slow for me, but I do use it when initially entering data just so I don't skip a step. I have often saved draft versions (whether pdf or ttax file) under different filenames to run various scenarios, but I still have the above-mentioned issues of hunting for the total tax (on Fed & multiple states) and creating a summary spreadsheet for each saved scenario.
Glad I asked! Thanks for the response.