Once you copy a game from the content library, you can make any changes you want to the game. The original game will stay untouched in the content library. You can’t, however, share the copied game back to the library for others to use even if you’ve made changes to it.
If you want to create a game which you share to the content library, make a new game on your dashboard. You can still look for inspiration from other users’ games. You can also bring individual exercises to your game from other users’ games by searching exercises from the library. You can edit these exercises in your own game.