i am sorry, but the following response is from someone who is unsure what your question really is. please, if it does not answer you, would you mind including pictures of the armor you have and the armor you wish to change it to.
answer.
Ertheia like all races have skins for their armor, so if you have armor on ertheia, it will show up as liight or robe, although many armor sets appear to be heavy armor. as far as i know, there is no unique ertheia armor.
i obtained an immortal tunic from a warehouse, and added recovery.
i used an Ertheia character to add recovery. afterwards, i was able to equip the tunic with a non ertheia character no problem.
the only kamael exclusive equipment in the game are modified swords, and bows which you change back and forth through a kamael skill.
if you have armor with a specific subtype and wish to change it, and normal blacksmith will be able to perform this action for you. R grade set options, cost a bit of adena but you can change from recovery to magic.
if you still can't equip the armor, please provide screen shots to help me, or whomever maybe knows... how to assist you.