I haven't seen this listed in any documentation so I'm assuming it doesn't exist.
Shouldn't there be a method in the lua api to select the texture we want to use rather than just setting it in the register function. I understand this can cause some lag due to IO operations so the should be some customizations such as use another node's texture or store multiple textures and select later. We could use this and the metadata to make a node contain different types of itself rather than creating separate nodes, for example technic's battery box which uses 8 nodes just to display power level. I believe this will be very beneficial to many modders and open up more modding potential.
To summarise, I believe there should be a way to change textures of a node outside of the register command.
To actually change the texture the following options could be used - use another nodes textures/load from File system/have a table of textures to use.
Now if want to take it further maybe some way of creating textures on the fly, such as editing loaded ones or fully creating them.