There are no nickel plated AK carriers.
Those that look like nickel are just bright polished.
You can buy a new carrier and have it plated. Instead of the soft and easily damaged bright nickel, I'd go with bright polished hard chrome. It's FAR more durable.
The steel is polished before plating to give it the bright finish, not after plating.
Professional gun refinishers like APW/Cogan and Ford's usually offer mirror polish hard chrome.
If the carrier is deforming that much, something is seriously wrong. Either the carrier is soft or the hammer is mis-shaped.
All AK's will deform the carrier tail slightly, but this is usually self-limiting. It usually gets just so much and no more burring.
The carrier tail doesn't really reset the hammer, it's the slam fire prevention safety.
The tail prevents the hammer from touching the firing pin until the bolt is locked.
Continue filing on it and you will deactivate the safety feature and the rifle could slam fire with an unlocked bolt.