is there a way to use a NBT tag to change the model armor uses?

Short answer: No.

Long answer: NBT can not change the armor model directly, but you could get an 'entity' with the armor model to spawn on/in the player* when the player wears said armor (a separate entity would be needed for each armor model). But this has its own issues like model rotation and walking animations. This can't be done in another way purely with Mcreator.
(*I really recommend "creating new armor" for each model. It's the same thing without extra steps.)
Replacing the old armor with new armor will work when keeping the same NBT and durability. It just sounds so much easier than diving into coding in my opinion.