So I was messing around in Waypoint and found a neat little glitch. If you go to modify a core different than the one you’re using, and equip a piece of armor, then hit the body tab, the armor will now be displayed on the core you had equipped. For example, say you have Yoroi equipped, but you want to see what the Willow Tea armor coating would look like on it, go to armor. Then highlight Mark VII. Go to modify. Then go over to armor coatings and equip Willow Tea (you don’t even need to have it unlocked). Then hit body, and you’ll get to preview Yoroi with the Willow Tea coating on.
Here is a link with some combinations I tried out. It seems to work for anything.
In a semi-related note, this shows that armor coatings do work on any core with no additional work.