Is it possible to exclusively enable CI for specific branches NOT via .gitlab-ci.yml?

Problem to solve

There is some repos on Gitlab server A which I have no control on, with according pipelines in each repo. Then project splitted and it became necessary to create a new Gitlab server B where I have control, which has active continious mirroring repos from server A, but also some new specific branches with different app configs and pipelines that totally differs from server A – different Docker repos, different infrastructure to deploy to, sometimes different build process.

And after each update mirrored from server A in their branches I got started and failed unrelevant pipelines on server B which consumes compute minutes and provides incorrect pipeline status in repos.

For now we can’t disable mirroring and remove server A branches from server B because at least main part of development goes on server A and we will cherrypick/merge updates to the new branches on server B – except for pipeline configurations, of course. And as far as I know (and googled) mirroring will overwrite changes in source branches on target repos – so I can’t just remove .gitlab-ci.yml from them.

So the question is: can I made some configuration on server B to exclusively enable CI for specified branches?

Worse and unwanted option: can I ask server A’s admins to make some one-time addition to their pipelines configs that will not affect their processes but prevent their pipelines from run on server B?

Steps to reproduce

N/A

Configuration

N/A

Versions

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