How to make a composer dependency commitable?
When you run composer install on one of your main projects, if you do --prefer-source you should then be able to CD into the vendor directory of your common-bundle, make changes and commit them back to it.
Can you add your commonbundle repo to each project as a git submodule?
cd /path/to/Proj1git submodule add path/to/commonbundle commonbundlegit commit -m "added submodule"[repeat for Proj 2]