Hypothetical NFA Item Repair/Replacement Question

[CharlieMike]

Lets say that you have a lower receiver that you used to create an SBR by filing a Form 1.

Let say said lower receiver is damaged in a catastrophic way like by faulty ammo or by being run over by a truck. It is so damaged that it can only be replaced or re-manufactured (melted down and re-forged).

Now, what recourse does the original manufacturer have for "repairing" this item?

Would it be legal for them to accept the damaged lower, re-forge it, and stamp it with the same serial number?

Would it be legal for them to accept and destroy the damaged lower and replace it with an identical model with the same serial number?

Again, this is completely hypothetical. It seems to me that it should be perfectly legal to do either as long as there are never two working lowers with the same serial but, this may just show my ignorance. I think ultimately, this is a question of if the serialized part of a firearm can be replaced or cloned.

ETA:

I got an answer from the NFA branch. It was pretty much, "NO! YOU CAN NOT CLONE A FIREARM! WHAT IS YOUR NAME AND WHERE DO YOU LIVE?" I'm paraphrasing. They were actually very polite and helpful. Now my question is why not?