I have "simulated" such a local manipulation of an original inside the catalog under ../originals.
Such change is not synced back to cloud, which is good, as we can assume at any time that the cloud file remains clean.
But Lr does not notify that a file is damaged locally and does not refresh it from the cloud back to the local catalog.
Means: if you at any time export such files from the catalog to put it somewhere else, you export the damaged file.
It would be an easy improvement, if Lr just tracks the checksums of the local files agasinst the clean file in the cloud to notify the user that local data corruption happened. A possibility to refresh the local file would be nice. Or is that already possible today and I did not find it?