I've been using MS since it was first released but until recently, I'd always managed to keep the number of patches in a concert below 128. However, I recently had to add a bunch of patches and because I use MIDI program changes from forScore to select patches in MS, I was wondering what I was going to do because the MS user manual is a bit vague i.e. MIDI PCs only accommodate 128 program changes and whilst I know that MS supports sending bank select commands, I didn't think it would support receiving bank select commands. Plus, there's no info in the MS user manual about what the MSB and LSB settings on the sending device need to be.
In any case, all you need to do is set the Bank Select (in the MIDI attributes pane for the patch) to a bank other than 0 and on the sending device, set the MSB to 0 and the LSB to the bank number corresponding to your MS patch. (Of course, you will also need to set the correct program change number) Voila...you can now use MIDI Program Changes for a LOT more than 128 MainStage patches.
This might be old knowledge for many readers but someone in future may find it helpful!