I noticed that a number of female NPS have Opposite Gender Animations specified in the ACBS record. Using TES5Edit to create an ESP containing override entries, I set the Opposite Gender Animations field to 0. I expected the default female animations to be used, but this has no effect and their animations are unchanged.

Is there something else I need to do or change to get this to work as expected?

Many thanks for any help or guidance.

Why would you want to?

Anyway, unchecking the box in the CK produces the expected results, assuming there are no later-loading mods overriding it. Try using the CK and then comparing it to the Edit-edited file and see if anything is different.