https://bugzilla.redhat.com/show_bug.cgi?id=1506428
--- Comment #9 from Andrew Toskin andrew@tosk.in --- THANK YOU. That step was not mentioned in the wiki page about splitting packages, and it didn't occur to me to treat the newly split packages so much like creating whole new packages from scratch.
However, now I have a new problem: fedrepo-req reports "Error: The Bugzilla bug's review was approved over 60 days ago"