I have not yet banged my head against the Eclipse manual hard enough to know this, so please excuse my ignorance: are these property modifiers specific to grid properties or can they be used for arbitrary keywords (e.g. wells stuff)?

Probably more relevantly, do the modified keywords need to be unique? (i.e., can they be identified by their name or can the same keyword appear in a deck multiple times? If the latter, I propose to add a variant of this method which takes `DeckKeywordConstPtr` as an argument.)