Allow overwrite when saving field matching

When you define a new field matching you often need a few tries to get the fields you actually want. If you check the "save this matching" you get a saved matching. Great. But the next attempt fails with "duplicate name", and I have to choose another name, polluting my list of matchings, which I need to remember to return to and clean up (which is in a completely different part of the "app").

A simple "allow overwrite" checkbox would greately ease this use case.