I've applied two overlays to the hopper block model that are dependent on the "enabled" blockstate. When the "enabled" blockstate is "true" it displays one overlay, and when it's "false" it displays another.

In-game, these overlays don't update until I right-click on the hopper or reload the world.
I've attached my resource pack's "hopper.json" as taken from the "blockstates" directory.

I've also done something similar with redstone dust so it displays a numerical representation of it's power level, and this works flawlessly.