Creating a block with dynamically assigned textures

Hi,

I want to create a block that can have multiple different textures, but have them dynamically assigned to the block.

Example:

A slab block that will, when right clicked with any other slab block combine into a full block, but with the textures of both slabs (so it looks like one slab is on top of the other, but inside the same block).

I can do this with blockstate and blockmodel files, but I am looking for a different solution as I want to add potentially 100s of slabs and that would obviously result in a huge number of blockstate and block model files.

So I thought, maybe I can create a block that holds the registry names of the two slabs its made up of as properties and then write something that applies the correct textures to the block.

I tried looking at the chisels and bits mod, as I thought that it must be doing something simmilar (storing the texture of each pixel of the blocks), but I didn't really understand how that works.

Could someone point me in the right direction or explain to me how this is done, please.