You can certainly run BiaB from an external drive, however, the bulk of the storage is in the RealDrums and RealTracks folders. You could just move those folders and their contents to an external drive, and use
Options > Preferences > RealDrums to set the name of the custom drums folder to your external drive.
Repeat with RealTracks.

That approach will mean that no other settings need to be changed.

Attached Files (Click to download or enlarge) (Only available when you are logged in)
2022-08-13_13-48-02.jpg (38.76 KB, 123 downloads)

BIAB & RB2025 Win.(Audiophile), Sonar Platinum, Cakewalk by Bandlab, Izotope Prod.Bundle, Roland RD-1000, Synthogy Ivory, Kontakt, Focusrite 18i20, KetronSD2, NS40M Monitors, Pioneer Active Monitors, AKG K271 Studio H'phones