The catch rate does work but 255 doesn't mean you'll always catch the pokemon. just that you have the most chances. Stuff like their current HP and stuff still apply to the catch rate, but if you drop their hp at least a little bit or paralyze them, it's an almost 100% catch with any pokeball
EDIT: the in-battle stat changes don't work. you can visually change them to lv6, and if you try to power up, the game says "can't power any further" but the actual buff is not applied. Tested this out and noticed my attacks always do the same damage no matter what I set it to.
EDIT 2: However the base stats /exp yield / abilities part works for both sword and shield.
this topic's name could get changed, it works in both. And what doesn't work, doesn't work in both. This table is genius.