For me there are different solutions to this, it depends on this other system what it is and who is the owner of the data (MEGA or the other system)
based on the information given, I do assume that MEGA is not the owner of the related-screen information, but the other system is having data ownership on this. If that is the case, I would maintain a catalogue of those screen objects in MEGA which is automatically updated via a batch program that runs on daily/weekly basis overnight (depends on the update frequency regarding screen objects) and I would prevent MEGA users of creating such new screen objects via metamodel access.
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