Programing Action Keys

It's not really clear what you are trying to do. Muse score handles transpositions automatically if you have selected the correct instrument, see https://musescore.org/en/handbook/3/create-new-score#instruments-and-vo… andhttps://musescore.org/en/handbook/3/transposition#transposing-instrumen…, or if not then there is the transpose tool, see https://musescore.org/en/handbook/3/tools#transpose.

If you come back and attach a sample score and describe in more detail what you are trying to do, someone can probably suggest an efficient process.

There are definitely third party programs out there that let you build macros like this. Also, one can create plugins in MuseScore, and there is even a plugin that allows to create macros - see https://musescore.org/en/project/action-chain-shortcut. That last one should allow you do pretty much exactly what you describe.

But also, it could be there is a better solution still. If you're transposing for horn, you shouldn't physically transpose the notes, you should really just change the transposition of the staff (in staff/part properties). Or change the instrument itself. Then MuseScore transposes for you automatically, and even allows you to toggle back and forth via the Concert Pitch button. This isn't necessarily fewer clicks than literally transposing the notes, but it's the better way logically, and might also be automatable.

If you attach a sample score and describe the goal in more detail, we may be able to suggest more efficient methods.