@jrsphoto For testing, I have folders in the sys folder named RRF2 and RRF3. These hold config files specific to each firmware version, including homing and tool change files; basically all the .g files. In the main sys folder I have a simple config.g that switches between these using M505 Set configuration file folder:
M505 P"RRF2"
;M505 P"RRF3"
M98 P"config.g"
The sys folder also holds the iap files (used for updating firmware), the firmware .bin files and the heightmap.csv file. When I want to switch firmware, I edit the semi-colon comment mark in front of the relevant command in sys/config.g, and upload the firmware binary that I want to use, and allow it to install the firmware. The Duet resets after flashing the firmware, and runs the relevant config.g file.
Using this you can experiment with RRF3, while maintaining a working setup with RRF2 you can swap back to.
Edit: FAO @jens55 too!
Ian