hi, modifying game folders can change client side things and pretty much resource packs, you could make ur sword sound like a cat or smth by changing the audio, but i wouldn't advise it cuz sometimes when you modify some visual folders (like how i make my brightness go above what Minecraft normally lets you) it can send packets and if im right the CubeCraft anticheat uses packets to find hackers and (once again like myself) you can get falsely banned.
Yeah you're allowed to edit your brightness to be brighter than vanilla. As well as using a resourcepack to change the look of items and sounds, as those will only change for you. As long as you're not getting an advantage over players when it comes to physical modifications like the combat or flying. Those would be cheating modifications. Resourcepacks are fine.
