In I Will Fear No Evil the protagonist undergoes a brain transplant from his old withered male body into a beautiful young female body, and hir personality shifts from aggressive alpha male to manipulative female who gets hir way by acting as if s/he were extremely submissive. S/he also experiences hir first female orgasm via a bare-bottom spanking, and concludes that female orgasm is a lot better than male orgasm.

In Friday, the female enhanced human protagonist is gang-raped and enjoys it with one of the perpetrators, who in the end turns out to be another enhanced human who only raped her because he "had" to - and they fall in love.

In Stranger In A Strange Land, the Heinlein stand-in, Jubal Harshaw, lives with a non-sexual harem of beautiful young women who alternate serving him when he shouts "Front". Eventually these women become a sexual harem for the putative protagonist, Valentine Michael Smith, who dominates everyone he comes in contact with through a combination of charisma and Martian magical abilities, including telepathy and the ability to alter someone's physical state through his mind alone.

In Glory Road, the male protagonist keeps the female Queen Of The Universe in line by threatening to spank her with her own sword - but apparently she has a hard limit about being spanked with HIS sword, God knows why.

Hope this helps.