1. Login to cPanel
2. Under the Security section, click on Modsec Manager.
   
3. mod_security will be on by default for all your sites, shown by a checkmark beside them.
   
4. Remove the checkmark beside the domain you wish to turn mod_security off for, and click Update.
   
5. You should now see that mod_security was disabled for the domain you selected.
   
6. If you have mod_security disabled, you'll see a blank checkbox beside the domain.
   
7. To enable mod_security on a disabled domain, place a checkmark beside the domain and click on Update.
   
8. You should now see that mod_security was enabled for the selected domain.
   

You should now know how to turn mod_security on and off for any of your domains that might be encountering problems relating to it being enabled by default.