not really. if all saves has posted in a version before the Molten Dmnd update into a new element called "IDES(indestructable)" that WILL NOT break older saves, while new kind of saves can be maked.
You technically CAN make molten diamond through console commands
Just think of it this way:
People use DMND because it is the ony unbreakable element besides the WALL group. I you were to make them breakable, then what element can people use to be indestructable.
electrode (except for protons), void (kinda useless for this), and I think there are others, just cant remember them all.