Okay basically he can move between different people in his canon using their neural implant ports which is something that's specific to him and the AI he was originally part of.

Specifically he usually runs Carolina's armor and more or less is in her head all the time but he's also been seen popping in and out of other soldiers like Tucker and Caboose. He doesn't do it to just anyone, though. They're kind of his team so it's sort of an understood thing. But basically, he could probably pop into any Freelancer, Red or Blue if he needed to.

Obviously not without permission from said player, but generally, it'd just be Carolina, especially if he has a body to use during downtime.