I don't think he's planning on registering it, more likely wanting to have some docs to shortcut any possible future case if he wanted to quickly show that he had it built prior to 10/1.... (rather than wait for the state to attempt and fail to prove he built it after)
But I didn't think the separate items were banned, but the sale and transfer of a rifle with those features. Lowers will still be available and allowed, just not complete in the current configurations.