I've gotten most of the mistward armor on one revenant but also want it for my boosted Charr revenant. Am I able to get the armor set on my boosted charr rev somehow or do I need to re-do the acheviements?
Go to your hero panel and click wardrobe. You can use transmutation charges to change the appearance of your armor.
Edit: stupid autocorrect on phone
The skins should be unlocked in the Wardrobe. The actual armor pieces are soul-bound once used, so you would have to do the Achievements once more for another set.