Custom item texture don't work
Model: bedrockiumingot.json
Config: customItem.json

I have to repot the same issue. Also, when I list all items by minetweaker, I am reading strange behaviour:
My new Item in customItems.json "name":"coin" is registered in minetweaker as customitems:item isn't it strange? BTW, the version is also 1.10.2

To add to this topic,
when I add second item,
mine tweaker sees only the first one, even those minecraft has both registered.
Adding the customIems.json to be clear:

{"data":
	[
		{
			"name":"coin",
			"rarity":"rare",
			"enchanted":true
		},
		{
			"name":"wood_rod",
			"rarity":"common",
			"enchanted":false
		}
	]
}

that behavior is normal, all basic items in CustomThings share the same item object, they just use different damage values. To specify them in MT you need to use damage, so it would be customthings:item:1 for instance.

Fixed via 08df8cb