It's understandable that you shouldn't be able to literally undo but to have step back / forward control through the app would be a welcomed improvement.
I'm not sure what you mean. What's the difference between "undo" and "step back"?
We're likely thinking of the same end goal, but I took the literal defintion of "undo" in that it "undoes" something. If it's a true undo (removing something from a stack), then stepping forward again would have a different outcome which is undesirable in this case.
However, if it's a simple history list that you can step back and forward through, then that would be great. Arguably the log achieves this goal, but it is lacking and removed from the game play. Simply having a back to reopen a dialog box you accidentally closed telling you to test some stat, and then a forward to move back forward through this history would be quite nice.