Can you re-enable cheats on a world?

I accidently disabled cheats on a creative testing world, and didn't notice until now. I put a bunch of stuff in it already, is there a setting in the level.dat to turn cheats on/off? If so, how can I edit it?

###EDIT: NBTExplorer saved the day. Thanks, u/BellLabs.

EDIT 2:

• 4 people said

Open to LAN

• 2 people said

NBTExplorer

I heard you guys the first time. No need to repeat the same comments over and over again.