Kotor I - More then 20 Level Ups!
Reason: Only recently did I choose to hold off on level ups in the beginning of the game so I can get more force powers. I use to go 8 or 9 level ups, now I wait until 3 or 4.
There are tons of awesome feats and powers and I get like barely half. Also, by the time I need those certain powers and feats at their strongest its too late. And I always run out of level ups by the time I reach the Unknown Regions.
Kotor II - More Lightsabers!(like in kotor 1!)
Reason: I love the new ability to convert your team mates into Jedi/Sith. So, why not have plenty of lightsabers to go with them. I can't remember before, but I'm currently playing and only have found 3, plus the one I built. I've got Kreia, Visas, Mical and Atton with the ability to use the force and a lightsaber, don't have enough. And all that I've collected are double blades, so, everyone fights and looks the same, kind of boring.
I know you said change 1 thing, but like some of you above, it would of been nice if they had a few more worlds to travel to. It can take time to convert your team mates and by the time you are powerful enough you're near the end. Also, I know in the first game you have 4 worlds to find the star maps, but that didn't mean only 4 planets in the second game.
When I first played and saw, I believe that was old Coruscant, I was hoping to go there and see whatever destruction the place had. And Korriban feels kind of like a rip off since there aren't many side-quests and its very fast. I wasn't too fond of returning to Dantooine. There are hundreds of worlds listed for the Star Wars universe. They should of picked some new worlds.
"I've got a bad feeling about this!"