This might be most requested feature still open (besides poly and expanders, which are in the works).
I started working on this. Instead of having a separate yml file, we can use the existing settings file. There can be a global setting in the prefs to enable/disable this. To assign patches from within MM, a new menu item appears under “Startup Patch” in the PatchView File menu. Choosing that opens a pop-up where you can select a MIDI PC# and MIDI channel. It will auto-increment to the first unused slot, and display the existing assignments so you can choose to overwrite (or not) an existing entry. We might need a way to view all assignments at once, which logically would go under the global enable/disable in the preferences.
Or if you have a ton of patches to assign to PC’s, or you just prefer to write it out by hand, you can edit the file on a computer by doing System > Backup Settings to Disk, edit on your computer, then System > Load Settings from Disk