Levels can be manually edited for extra right-click values for entities. In SE, it can also be used to clean up deleted enemies that normally cause the game to crash.
Manually editing the game's options allows players to set player colors to very precise values, change key binding outside of the game, and even set which levels are unlocked in a mappack.
The only way to rename animations is to change their filenames with a file viewer.
As there is no in-game editor for Custom Enemies, the only way to create them is through Text Editing.