We don't care about master branch we work only on release-x.x branches
In this example we will create the release 6.6.0 containing our license changes
0/ Be sure to have official MM git repo as remote
git remote add mattermost git@github.com:mattermost/mattermost-server.git
1/ Fetch all changes and create new branch from official repo
git fetch --all
git checkout -b release-6.6 --track mattermost/release-6.6
2/ Reset branch to commit tagged to the version you which. It's generally few commits behind
git reset --hard e05e0f9379e1324618601e3ba6111d78710e6319
3/ Apply our changes
git cherry-pick d68ae55e015e426f1ceb251d13db144d5e934e65
4/ Overwrite MM tag to our commit
git tag v6.6.0
5/ Push branch and tag
git push origin release-6.6
git push origin v6.6.0
TODO
Check setup step in the Drone build and make sure the script if fetching correct branch of the webapp and not master or other
+ bash .drone/setup.sh
Cloning into 'mattermost-webapp'...
Branch 'release-6.6' set up to track remote branch 'release-6.6' from 'origin'.
Switched to a new branch 'release-6.6'