You can add a texture to each damaged value on a diamond chestplate (ex. you make it a obsidian chestplate) but when you put it on it just looks like a diamond chestplate. There should be a tag when changing the model for what it looks like when worn. This can be done in the .json txt document for the model the diamond chestplate is being overridden to.

I made this because it bothers me that I have a re-textured armor piece but when I put it on it still looks like the original piece of armor.