Mike Mika's five-year-old daughter wanted to play Donkey Kong as Princess Toadstool, so he hacked the ROM to effect the genderswap (see the Damsels in Distress episode of "Tropes vs Women in Video Games" for more). He's even posted a patch (ZIP) for the original ROM so you can play it yourself, or with your kids.
My three year old daughter and I play a lot of old games together. Her favorite is Donkey Kong. Two days ago, she asked me if she could play as the girl and save Mario. She's played as Princess Toadstool in Super Mario Bros. 2 and naturally just assumed she could do the same in Donkey Kong. I told her we couldn't in that particular Mario game, she seemed really bummed out by that. So what else am I supposed to do? Now I'm up at midnight hacking the ROM, replacing Mario with Pauline. I'm using the 2010 NES Donkey Kong ROM. I've redrawn Mario's frames and I swapped the palettes in the ROM. I replaced the M at the top with a P for Pauline. Thanks to Kevin Wilson for giving me the lead on the tools and advice.