To my understanding, EZSkin will do either/or, not both.  If the textures do not have any bump mapping, you can elect to create a procedural set.  If bump mapping already exists, you can elect to continue using the original or have it replaced by a procedural set.  The third option, have the script decide for you; create a procedural if bump mapping doesn't exist or default to the original bump map if it is already there.