Can't use Blockstates with java model / How to change textures of an animated block w/out multiple blocks?

I was wondering why the new blockstates section seems to be getting disabled whenever I use a java model?
The reason is because I wanted an animated model w/ changing textures without needing multiple different blocks, but I can't seem to figure it out.

Is there another way or workaround that doesn't need multiple blocks & doesn't need giving up animations, even a plugin, or is there not?