Ok, so I want to make a mod where you can enable/disable glass visibility. My idea was to either replace the texture of glass, or change the opacity if possible. I can't really seem to figure out how though. I  tried replacing the BlockGlass instance in the Blocks class with a custom class that extends BlockGlass, but it's a final field so I can't modify it.

 

Does anyone know how to do this?

You can replace the block with GameRegistry.addSubstitute (or something like that).

Thanks, will try