how do i turn off cheats on specific levels

What do you mean cheats

like fly, noclip, speed, ect?

You need to change the motd

to turn off hax on your own level, do

/os map motd -hax

Note: You wont be able to do it if you aren't the realm owner of that certain map, but if you have access to /map (which allows you to edit map options on any level) You can do 

/map motd -hax