Puresteel Paladin has two abilities, the second of which is a metalcraft ability that changes what you can pay to attach equipment you control to creatures you control. It does so by giving your equipment an additional equip ability that costs zero mana. This ability does not alter the cost of existing equip abilities or remove them. This means that you can pay the equip costs of the original equip ability. In most cases, you would probably not want to. However with something like Piston Sledge you may if you wanted to get rid of an artifact you control, like Ichor Wellspring.