Improved Custom Textures

I couldn't add Custom Textures for blocks, as they don't have the NBT tag "CustomModelData". Also, you can only use the texture override for items with just the "CustomModelData" NBT tag, instead of other NBT tags as well, which is a little confining.
There are some exceptions, like note blocks and double slabs, but those are annoying to use.
Perhaps, instead of adding a whole new tag to every single block, there could just be 2 types of new blocks; a Template Block and a Modifier Block. 
The Template Block should hold an NBT tag of 'Custom', and using a texture pack, you can modify their custom texture using this tag and it's value. An example of this is, a Template Block with the value of tag 'Custom' as 7 could resemble stone bricks (/give @s template_block{Custom:7}), while the Template Block with the value of tag 'Custom' being 8 could look like a grass block (/give @s template_block{Custom:8}). You could edit the textures and model of what the Template Block has through modifying the block models of it inside the texture pack's folder, like with Custom Items and the CustomModelData value + CustomModelData predicates. Finally, the Modifier Block could act as a Repeating Command Block, constantly running, in which you can change the hitbox (from Full Block to Slab to Wall to Rod etc), break speed & tool, drops, necessary environment (like sugar cane needing water), model and so on depending on the 'Custom' tag of Template Blocks. This would greatly benefit mapmakers!