Suggested by Dynious, thought I'd post this here so we don't forget about it. Still need to figure out how to do it.

After a lot of frustration, I'm making some good progress on this:

Still some stuff to figure out, though.

Could you post add this to a branch in your fork so I can follow your progress? I'm very interested :D

Sure, you can check it out here: https://github.com/squeek502/BlockExtenders/tree/rendering

Any progress on this? I would like to have this feature in the next release :)

The disguising is pretty much fully in place/working except for grass blocks, but even Extra Utilities' drawbridges have incorrect coloring when disguised as a grass block (however, to get around the problem, we could hard-code the sides/bottom of a grass-disguised block to show up as normal dirt).

The last thing that needs to be figured out is how to set/clear disguises. We could re-use the linker for it if you'd like (right click the block you want to disguise as with the linker, then right click on the block extender to disguise as the linked block; right click in the air [or maybe shift+right click] to clear the linker, right click a block extender with an unlinked linker to clear the disguise), but I'm not sure if you had something else in mind.

I think shift-right clicking with the to-be-set block on the connected face of the Block Extender should be good enough, shift-right click with an empty hand should clear the disguise.

Shift right clicking with an empty hand currently toggles redstone transmission.

Oh, yea, I forgot about that. Let's then do it the way you described in your previous post.