It allows you to swap the xdp reference to a completely different one though e.g. from Test.xdp to ABC.xdp, that would have the same potential problem of leading to binding errors. I think we both agree that changing things in the JCR manually is a last resort, but given a lack of an alternative in the UI it is the workaround I would use.
I would still be keen to get someone from the forms development team's opinion on whether this is something that should be added to the UI.
I am from Adobe (not from Forms' Engineering Team), so not an official word. But as far as I know changing the Form Model will lead to binding errors on all the bound fields, this may be an important reason to not allow it in first place.