Scores originally written in MuseScore 1 continue to cause problems. (Transposition of B-flat trumpet)

I have a collection of scores that I originally wrote in MuseScore for B-flat trumpet, which have been converted through all the different versions of MuseScore up to version 4 (receiving various edits over time). These scores have caused me problems before (see https://musescore.org/en/node/319769), and this week I ran into another new problem.

This week's problem revolved around transposing. I decided to transpose one of my songs down by a perfect fourth. The piece originally had a key signature of C (this is what appeared on my B-flat trumpet staff). When I transposed down a 4th, I was expecting to land in the key of G (one sharp), but instead ended up in the key of A (3 sharps), along with accidentals on some notes.

I also had a problem trying to "Respell Pitches" on the original score. "Respell Pitches" will turn the C-natural at the end into a B-sharp.

I note that viewing the piece in concert pitch and then transposing does the transposition correctly.

I tried exporting to MusicXML and reimporting, but that did not solve the transposition problem. So I resorted to inspecting the XML of the misbehaving score, so that I could automatically edit it manually. I found that the XML identified my instrument as an e-flat Cornet.

Comparing with other scores that did not come from MuseScore 1, and were both wrong. I wrote up the attached python script to fix my scores.

As I already mentioned, this isn't the first time my MuseScore 1 scores have had wierd issues that MuseScore 3 and 4 couldn't handle.

Is there any automated way to fix these scores and remove other issues (which I haven't identified yet) that might have cropped up as a result of converting them from MuseScore 1 format, essentially rebuilding them from scratch in an automated way? There are roughly 50 of these, so fixing them manually would be a pain. And while I understand how to edit the XML in the future if a new issue crops up, I'd rather not keep playing whack-a-mole with new issues.