The answer to your question is only available to Authorized persons. A couple years ago I saved this address and faq question and answer-
https://www.atf.gov/firearms/qa/may-...urposes-intent
May the short barrel on an SBR or SBS be replaced with a long barrel for hunting or other purposes, with the intent of replacing the short barrel?
Yes, and you will not be required to again register the firearm before replacing the short barrel. ATF recommends written notification to the NFA Branch when a firearm’s configuration is permanently changed or removed from the purview of the NFA.

I just tried the link and got this-
"Access denied
You are not authorized to access this page."

So I don't know.

It makes me think that there is a Deep State infiltrator screwing with people.