Merge between projects?

Is it possible in gitlab to merge between projects?

My organization uses the Drupal CMS on all of it’s websites, and it’s become quite a pain to have to manually update each projects core files one by one. We would like to setup a system where we have a single project/repository that houses all of the latest updates and security patches for the CMS, and from there we can merge that into all of our other projects at specific branches.

Is it possible to do this? If not directly, can we use some sort of hook system to automatically pull in the latest changes from another repository?