There are several factors that coincide with the 922R process. You will need to contact ATF or local law enforcement to see if you can install this extension and be compliant.
922R is for when it’s getting imported. This has nothing to do with people who purchases. It used to be an issue when people were importing parts from others countries for AK. At that point you are the importer and must abide by 922R.
https://www.atf.gov/firearms/qa/i-possess-pistol-which-was-imported-and-then-subsequently-equipped-stabilizing-brace
ATF explains the law in detail.