Well that depends on your viewpoint...
My codebase was derived from osmocom max branch about a year ago, so strictly speaking it is a "fork", but it's also the production version which I maintain and enhance.
If you are already using the boatbod version of op25, the simple way to pull the updates is to run a "git pull" command from anywhere inside the ~/op25 directory hierarchy. If you're on the osmocom or dseven versions, you'll probably be best off to clone a completely separate version from my repo much as if you were installing from scratch.
cd ~
cd ~/op25.boatbod
./install.sh
(Once installed you can copy your config files over from the other version)