Well, I was doing the same thing as you, but I think I realized why my tests went awry. I was trying to add cloth gloves to the fortify alteration enchantment. However I now think I was adding the word for greaves. So I took a look at your plugin and I couldn't enchant my gloves with alteration. So, I think there's a different selector for each type of body covering.
There's armor and clothing for each part. Or so it seems to me.

Yeah, there's ArmorHelmet - ClothingHead, ArmorGauntlets - ClothingHands, ArmorBoots - ClothingFeet and ArmorCuirass - ClothingBody. Plus ArmorShield, ClothingRing, ClothingNecklace and ClothingCirclet. I just added all 12 types for all enchantments. Might've missed a record or two, will check.
I was adding (ArmorGauntlets) instead of (ClothingHands)
EDIT: It appears you did add (clothinghands) to the alteration enchantment. Hmmm, why can't I enchant the gloves then?
Actually, I think these gloves were added by a crafting mod. Could that cause an issue?
Probably. Could also be that the interface isn't updating. Try exiting from the enchant table and reopening.