your always always aloud to do what you want, as long as there is a reason for it... like lets say putting a metal on metal, would dignify a alignment to something more then wealth and would command extreme presence on the battle field. I mean the whole point of them in the first place is to identify your allies from the enemy, so even in fantasy they should follow a least a loose set of conventions in order to make your fantasy world more "believable".

And knowing the original rules may inspire some awesome things!