I remember watching the Man Show and seeing Jimmy doing blackface. It had an edgy, transgressive vibe even back then -- Jimmy knew it was offensive. The humor was in the shock of breaking a taboo. He was inspired in this by Howard Stern, who also donned blackface, and also, like Jimmy, dropped the n-word " ironically ".
It was the era of the "shock jock". It's not a case of Jimmy "evolving and maturing", imo, but of changing cultural fashions. When being sexist and racially transgressive in a self-conscious way was cool, Jimmy was those things on TV. When cultural attitudes changed, so did Jimmy.
No enduring principles, just going along with the zeitgeist.