I've gotten some help in the MMD Discord, but I'm still not fully understanding what my JSON files should look like after using the mesher to register item variants. This is my registration code:

 

 

 

// Model registration
          for(BlockGenericSkull skull : genericskulls.keySet()) {
                HeadItemMeshDefinition meshDefinition = new HeadItemMeshDefinition(skull);
                ItemBlockSkull item = (ItemBlockSkull) skull.getItemBlock();
                ModelBakery.registerItemVariants(item, meshDefinition.defaultModelResourceLocation);
                for (int i = 0; i < skull.texCount; i++)
                {
                    ItemStack stack = new ItemStack(item);
                    stack.setTagCompound(new NBTTagCompound());
                    stack.getTagCompound().setInteger("TYPENUM", i);
                    ModelBakery.registerItemVariants(item, meshDefinition.getModelLocation(stack));
                }
                ModelLoader.setCustomMeshDefinition(item, meshDefinition);
            }

And this is my ItemMeshDefinition:

 

 

package its_meow.betteranimalsplus.client;

import its_meow.betteranimalsplus.common.block.BlockGenericSkull;
import its_meow.betteranimalsplus.common.item.ItemBlockSkull;
import net.minecraft.client.renderer.ItemMeshDefinition;
import net.minecraft.client.renderer.block.model.ModelResourceLocation;
import net.minecraft.item.ItemStack;

public class HeadItemMeshDefinition implements ItemMeshDefinition
{
    public final ModelResourceLocation defaultModelResourceLocation;

    public HeadItemMeshDefinition(BlockGenericSkull head)
    {
        this.defaultModelResourceLocation = new ModelResourceLocation(head.getRegistryName(), "inventory");
    }

    @Override
    public ModelResourceLocation getModelLocation(ItemStack stack)
    {
        if(stack != null && stack.getItem() instanceof ItemBlockSkull && stack.hasTagCompound())
        {
            return new ModelResourceLocation(this.defaultModelResourceLocation.getResourcePath(), "type=" + stack.getTagCompound().getInteger("TYPENUM"));
        }
        return this.defaultModelResourceLocation;
    }

 

How should my JSON models look? I only want to change my texture, not transforms/models using the NBT data. Do I need an "item blockstate"? How should it look?

I don't really have a base of the JSONs to work off of, otherwise I would link them too.
Also not looking for recommendations on how to do it another way, currently sticking to NBT as it works best for my project and won't be removed in 1.13 (metadata).

Are you trying to do something like I did here?

https://github.com/Draco18s/ReasonableRealism/blob/1.12.1/src/main/java/com/draco18s/ores/item/ItemRawOre.java

https://github.com/Draco18s/ReasonableRealism/blob/master/src/main/resources/assets/harderores/blockstates/orechunks.json

11 minutes ago, Draco18s said:

Are you trying to do something like I did here?

https://github.com/Draco18s/ReasonableRealism/blob/1.12.1/src/main/java/com/draco18s/ores/item/ItemRawOre.java

https://github.com/Draco18s/ReasonableRealism/blob/master/src/main/resources/assets/harderores/blockstates/orechunks.json

Yes, and a good example of how my blockstate should look. I can try it when I'm at my computer but my mesher registration might not be right. Does

new ModelResourceLocation("registryname", "type=1");

work as a valid location to get a variant with the type attribute with the value 1?

https://github.com/Draco18s/ReasonableRealism/blob/1.12.1/src/main/java/com/draco18s/hardlib/client/ClientEasyRegistry.java#L147

19 minutes ago, Draco18s said:

https://github.com/Draco18s/ReasonableRealism/blob/1.12.1/src/main/java/com/draco18s/hardlib/client/ClientEasyRegistry.java#L147

How do I register using NBT values?

You need an entirely different system for nbt.

 

https://github.com/Draco18s/ReasonableRealism/blob/1.12.1/src/main/java/com/draco18s/industry/item/ItemCastingMold.java#L87-118

https://github.com/Draco18s/ReasonableRealism/blob/1.12.1/src/main/java/com/draco18s/hardlib/client/ClientEasyRegistry.java#L185-195