As far as I'm aware, they're not Imperial Grenadier guard's which mean's he can use this just so long as he doesn't use our tags 1er_Gren. However like I said they arn't Grenadier's so I don't see a problem here.
We cannot own the name "1er" it just mean's first in french, as many of you know I'm sure.
Thankyou Lawbringer and Day for trying to help out but I don't think there is a problem here, unless I'm wrong and I'm missing something.