I would change how cruel some of the other characters treat Jimmy in some of the eps (ex. N-Men, Eggpire Strikes Back, also the end of A Beautiful Mine-why did they all get mad at Jimmy at the end? They were forced to use their rubies as fuel to not die...smh). I questioned the writers' choices in some of these eps.
Also, I wish they showed more of Sheen's and Libby's home life/family. Like mentioned what happened to Sheen' mom, what his grandma looks like, etc. I really loved El Magnifico because it showed how much Mr. Estevez cares about Sheen. We barely see Libby's parents and know that she has a brother, but it would be cool if the show had more of Libby in general.
I also wish that the characters clothes changed sometimes especially when they are in cold weather, space, etc. It always made me feel cold seeing the gang in the snow and in space w/o jackets on.
Well, I might add more later. That's all I can think of for now.