I think some of these were already covered, but here's some changes I found out so far that some people may not know of:
D-tilt: Rosalina's head doesn't have a hitbox anymore, so instead you have to tilt the control stick slightly backwards so Luma can D-tilt the opposite way to cover rolling option.
Up-Smash: Luma's Up-Smash is now stronger than Rosalina's (I tested this out in Training Mode).
D-Smash: There's more cooldown now so there's a better chance you'll get punished doing the move.
Luma Shot: Distance is A LOT shorter when you tap B and doesn't have a lingering hitbox at the end anymore. When calling Luma back to you it retreats MUCH faster. Also, I may be wrong but when Rosalina waves her wand to call Luma back, the wind blow effect when standing in front of Rosalina seems to blow people away a bit further.
N-air: Definitely does 7% at most instead of 10% like it used to. Also the knockback is definitely A LOT weaker (R.I.P. my most used move
).
Grab: Idk how much damage her pummel did in ver. 1.0.3 but it does 2% in 1.0.4. Did her pummel get stronger or is it just me?
Overall I find the changes so far very sad and kinda unnecessary imo. I didn't mind Luma taking a longer time to respawn, but I never expected many other changes to her aattacks. Hopefully this won't stop people from playing Rosalina and Luma because I'm still gonna main her no matter what.