file off the serial numbers

verb2

1. •
   To alter identifiable details in a creative work in order to conceal its origin.
2. •
   (slang) Especially, to remove the copyrighted elements from an existing work of fan fiction so that it may be commercially published as original fiction.

   • I say “may have” because [E. L.] James has “filed off the serial numbers” of her fanfic. — 2012