just got back from a short holiday - will get onto that PR soon.
But to answer your question, it should be fine to merge the head back into the PR branch.
What is likely to cause problems, however, is if you keep working on that branch adding unrelated new features (ideally 1 PR = 1 branch = 1 small and self contained set of changes). If you want to make multiple unrelated changes and use them all before they are merged into the upstream I’d recommend the following strategy:
- create a feature branch for each new feature that will become a PR
- create a throwaway ‘dummy/testing/lab’ branch which you track on your computer (with the intention that this will never be merged into the main branch).
- merge your PRs and/or the main branch as needed onto the dummy branch
This should work well as long as you
a) never make any non-merge commits to the dummy branch (this requires a bit of discipline with changing branches before you make a tweak etc, although git is moderately forgiving here - if you forget you can change branches before you commit - it might be possible to enforce this with pre commit hook)
b) spawn new branches from the main/master branch rather than the dummy branch