Frost armor apply a debuff to the enemy who attack, the slow part seem to be part of the spell , the only thing you can with it go into gameplay constant and change the "frost effect" and change frost effect on attack/movement, however that will apply on all frost attack like nova, arrow,armor.
I dont think removing the buff will do anything at all.
How do I take the cold efect of of Frost armor so it wont slow down enemy units when they attack me?