Mmm Dealers.........
I had an aftermarket nudge bar fitted and had a similar problem with the grille.
As you said
all they need to do is unbolt the nudgebar leaving the mounting brackets exposed ,take the front bumper off, fit the grille, measure and then cut the grill in two places, insert and attach the bumper and griile thru the mounting brackets, then bolt the nudgebar back on.....
Good Luck with it let us know how you get on.