Is there a way to alter the list of Monk approved weapons?

[Negaman]

Hi all, please forgive my noobishness. I created some Brass Knuckles and wanted to allow my player's Monk to use them as part of the list of Monk approved weapons, but I can't find a way to alter it or to designate the Brass Knuckles as Monk approved. I tried searching the forums for this and I didn't see that anyone had asked about it yet.