The answer, is sort of... You can edit what gets replicated to the Global Catalog.
I can see no reason why this would be a good practice right now though. Active-Directory as a database should be the source of verifying identities between locations, not for storing mismatched data. If you want nick names, then use nicknames in a standard way that can be verified. If you want less visible attributes, then use hidden Extension attributes.
Active-Directory should be one of the places you know the data is correct and uniform.