Keeping individual .gitlab-ci.yml files in forks

Hi, i have a doubt that i cant seem to find anywhwre so i finally decide to ask here, in my scenario i have a project that serves as a base for other projects so everytime we setup a new one we fork the main one in order to avoid granulation and lack of upgradability of the projects, we have set a mirroring process so everytime a commit is made to the main project ‘master branch’ it replicates to all of the forks, and a obviously we can set a manual merge request in order to send changes from the forks back to the main project (if it turns out to be relevant for everybody of course) the problem lays now that we are implementing CICD processes because i cant find the way to tell in a merge request that a certain file shouldnt be included in the MR (.gitlab-ci.yml in this case) or a way to tell the mirroring proccess that do not mirror certain files, if somebody could point me in the right direction to manage this kind of situation i will appretiate it, again i didnt think to be the first one with this kind of issue, but i cant seem to find the info to solve it, thank you very much everybody.