A block in my mod has a texture for on and off but it will only update when the GUI is open.
the block code can be found here: https://github.com/danielm59/Fast-Food/blob/master/src/main/java/danielm59/fastfood/block/BlockChurn.java
the tile entity code can be found here: https://github.com/danielm59/Fast-Food/blob/master/src/main/java/danielm59/fastfood/tileentity/TileEntityChurn.java