Both of the things you suggest are possible!
Programmer instruments can be used to play loose audio files that aren’t built into banks. For an example of this, look at the programmer_sound example included in the FMOD API. Files stored outside of banks do not benefit from bank compression and encoding, but are useful if you want your game to be able to play arbitrary audio files supplied by players.
You can also distribute your FMOD Studio Project (or a stripped-down version of it designed for modding) to your players. Information on how to do this can be found in the Supporting Downloadable and User-generated Content chapter of the FMOD Studio User Manual.
Note that your company may choose to limit which assets and other content from your game are distributed to players for a variety of reasons (for example, to prevent unscrupulous actors from pirating your game’s assets, or to avoid competing with the commercial release of your game’s soundtrack)…