Example: Removing the One Ring

Adding this to your Game.ini should do the trick:

OverrideNamedEngramEntries=(EngramClassName="EngramEntry_OneRing_C",EngramHidden=True)

EngramEntry and PrimalItem names are in this list[docs.google.com] (not the skins).

Note:
If you want to prevent people from crafting the Skins, simply remove the POMESkins Engram.
There are no additional Engrams for the skins.