JEI shows recipes for enchanting and/or combining the mob charms in an anvil with enchanted books, but I am unable to enchant the charms or combine them in an anvil with enchanted books. Is there a config option for this that I'm missing?

Specifically I'm attempting to put Unbreaking (III) on various mob charms.

So I intentionally have unbreaking and mending banned from being applied to charms. I will take a look at how to possibly remove this from JEI/JER, but not sure if that's going to be that easy.

If you do find that it's not possible at this time, could you add something like "Cannot be enchanted" to the tooltip for the charms?