Joker decided to help out his friends first before going out to have his own fun.
Firstly, he altered Turian and Quarian genetics to make it so that they didn't need to eat dextro-food anymore. He then made it so that this genetic shift was discovered ages ago and spread through both species. He then, deciding to be subtle, made it so that everyone in the galaxy would eventually, naturally, lose their prejudice against AIs and only call AIs evil that were actually evil.
Like the Reapers.
"I think I'm getting the hang of this," he said. For his last major alteration, he added another 40 years to the lifespan of Salarians. "Okay. Major changes done for now, time to focus on my friends..."
Jacob was pretty content with his new fiancee, so he felt he didn't need to do anything there. Zaeed had tracked down his old enemy and finished him off, and was talking about retiring. Things were going great for the Krogan right now, and Thane was making peace with his son. James was content with his life, as was Ashley.
Although Joker was really fighting the urge to make her breasts and booty bigger, just for laughs.
Which left everyone else.
Shepard was his inspiration. But she was left with no one after Kaiden died, and wasn't willing to romance anyone else in the crew. Which was a shame, since pretty much everyone was in love with her... Maybe Kaiden could return from the dead? Or Shepard could be set up with someone else...
Speaking of Garrus... Garrus was a bro. He could use some love in his life. Maybe a bunch of sexy girlfriends...
Tali. Adorable, brilliant Tali. She deserved to have someone to keep her warm at night. ...Maybe Legion. The two were becoming fond of each other. Although Legion's body would need to be adjusted...
Liara, the current Shadow Broker, was always so stressed. Perhaps there was a way to make her work easier?
EDI was getting used to her new body. Perhaps he or Legion or somebody could help her adjust to the physical aspects of it...
Samara deserved to have happiness in her life. Maybe a certain hyper-genius Salarian could be inspired to come up with a cure for the Ardat-Yakshi condition that kept her daughters cloistered at a temple (and led one of them to become a vampiric sexual predator, eventually killed by Samara herself...)
Kasumi ended up destroying the information cube that held her boyfriend's mind. She regretted losing him, but she understood why the box had to be destroyed. Still, causality pretty much belonged to Joker at this point. Maybe he could come back from the dead.
Speaking of Mordin, he'd done so much. Joker had already 'tweaked' his brain so that he came up with a cure for the brittle bone disease Joker used to have before getting the Infinity Gems. Mordin could use some fun in his life that wasn't medical related.
Javik... Poor Javik was alone. He was the last of his kind. Maybe a 'lost colony' of Protheans could be found somewhere...
...Jack and Miranda. Kasumi had suggested it as a joke, but actually, it sounded kind of hot. The two of them hated each other. But it would be so hot for the two beauties to be falling in love with each other to the point where they couldn't resist making out when near each other. And it'd be hilarious if they just never understood WHY they were falling in love. (With some physical enhancements to their bodies, just for fun...)
Decisions, decisions...