The original NES version of Legend of Zelda was hacked by a fan named Imgurian jadowdl so that he could propose to his girlfriend. You can watch a video of how it all played out below.
It took him about a month of work to accomplish this feat. He altered some of the in-game sprites to resemble his girlfriend. He basically changed the ending of the game so that when they beat it on a full day run, it ended with a proposal. He says:
"Natalie and I met 6 years ago thanks to an algorithm I wrote while I was working for OKCupid. She's "The Geek Wedding Photographer", loves rabbits, and is the one for me. But it's really intimidating proposing to a wedding photographer - you have to get it just right! I've been agonizing for over a year.
"A highlight of our lives is getting together on the couch for play throughs of video games. The Legend of Zelda for NES is my all time favorite game. I got this ingenious little plan a few months back; I would schedule a play through with her, on original hardware, but have the game ask her to marry me when we beat it together."
You can read about his process of hacking the game here in case you're interested. It's pretty awesome that he was able to pull this off. Oh yeah! She said yes.