'Reimport with new source' command does not work on Mac.
Confirmed in 4.22 @ CL 4771381
PC/Expected: Anim is overwritten with new anim
Mac Result: No change
Output Log -> New page: Reimporting ThirdPersonRun.abc
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-68892 in the post.