Time signatures
I know you can add time signatures not in the palette by using shift + T, but adding such time signatures adds a new bar as well, whereas the palette signatures simply change the time signature at the selected bar. Consistency would be welcome. It would also be useful if these added time signatures were added to the palette for further use, even if it only applied to that particular score and disappeared when a new score was started.
Comments
For further use, you can save a time signature to a palette.
See:
https://musescore.org/en/handbook/3/workspaces#create-custom-workspace
and:
https://musescore.org/en/handbook/3/palettes#custom-palettes
Can you explain the first part? There should not be any difference between applying time signatures form the master palette (Shift+T) versus the regular palette. If you are seeing one, could you attach your score and precise steps to reproduce the problem?
My guess is you are getting confused y the fact that when changing time signature to something shorter, this necessarily it will take more bars to express the same amount of music, so MuseScore adds what is needed to avoiding deleting your music.
The origin of the time signature does not affect extra measures being inserted. If you insert a time signature that requires a shorter measure than the existing time signature, you will get extra measures. Try entering a 4/4 measure from the palette, then a 3/4 time signature 2 measures later, then put a 2/4 time signature in between and see the measures multiply by 2 in that section.