Just giving Luke and Leia each other's skillsets is the boring option, since all you end up doing is gender flipping two characters, which isn't the same thing as trading characters. Even if they were identical twins (which they're obviously not) they'd still be distinctly people and would react uniquely to identical stimuli.
So the fundamental question here is really: who are Luke and Leia once you strip away all of the history and baggage and up bringing. What are each of them at their core? What traits to they share? What traits do they not share? Once you have all of that you can apply that to the new situation and extrapolate from there.
So here goes with a quick & dirty outline; Luke is impatient, while Leia is calculating. Leia is empathetic and naturally selfless, while Luke seems predisposed to think of himself first and had to actually work on his empathy. Leia is brash and reckless, while Luke is often more risk averse when he's outside of his comfort zone. Luke is a dreamer, while Leia is grounded. Leia seems to be the more intelligent of the two but sometimes struggles to process her feelings, while Luke is more closely in touch with his emotions (for better or worse.) Luke's innate preternatural force talent is the same as Anakin's; precognition, while Leia's is like Ahsoka's & Yoda's; truth sense. The ability to intuit the truth of a person, both intent, and the truth they don't admit to themselves (just ask Niano Organa.)
They're both fundamentally courageous, have a clear sense of right and wrong, and will never flee from responsibility when it truly matters.
So to begin with Leia Skywalker (Lars?), since I think that's the more interesting though line: She never had the same natural affinity for flying as Luke, but she's as competent as any desert bush farmer needs to be. She's studied every tech old manual she can find, and can take apart almost anything and put it all back together, from the condensers to the family Landspeeder, and keeps her X-34 in perfect running order. Eschewing the kind of hot rodding Tank, Biggs & Fixer go in for in favour of proper by the book maintenance.
She's still part of that friend circle, but is more the loner of the group, much less willing than Luke to slack off and waste time when there's chores that need doing. Though when she was younger, she did have a tendency to wander off into the Jundland Canyons, or the rough streets of Anchorhead in search of a little excitement from time to time.
Never seeing eye-to-eye with Cammie, having no patience with Bigg's constant flirting, and being essentially invisible to Fixer. Tank is a bit of a blank slate, so there's any number of possible approaches from big brother figure, to potential crush, to the creep of the group. Dealers choice on that one since it hardly matters once he leaves for the Academy with Biggs, but never comes back.
Her affinity for people makes her an excellent haggler and deal-maker, and winds up brokering much better rates with the water sellers than the standard. By the time she's 16, she's the one running the farm's books, not Owen and Beru. As a result the farm does much better; Owen can afforded to hire extra hands out of Anchorhead in the peak seasons, and expand the farms holdings, even buying up some of old man Ulbreck's outer ranges.
That's all I got for now. I'll have to think more about Luke's path before I can decide how their stories might intersect.
