How Do You Change the Registry Name of Armor in the Code?

I am trying to change the item IDs of armor pieces, but when I try to, it removes the texture and changes the name to the language resource key. I changed the legs from turtlelegs to turtle_shellguards and, I didn't change the chestplate and boots and they work fine with the wrong item ID.

Here's my code

https://pastebin.com/NuRmzp99