Seconded - no overrides.
If the override is to a Catalog Pgf Fmt, sooner or later (usually sooner), someone will update the format elsewhere in the document, and do an Update All: bye bye overrides.
The alternative, however, is catalog pollution, or using scattered non-catalog formats (uniquely name, apply and delete from cat).
One solution is to define a Pfg Fmt, say "Overridden", that is only ever used when it has local overrides, and all the maintainers know that they are never to do an Update All on that format. This will still have downstream CSS consequences (not an issue for us yet).
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