Security preferences not remembered

I’m trying to install uktvnow onto my M8S Kodi box, I went to change the settings for apps and downloads, I believe a reboot is in order after this? When I have rebooted, the apps verification defaults to ‘on’. There seems to be no way around this that I can find, in all fairness though, I’m quite new to these boxes so maybe there’s another trick to try?

Any help greatly appreciated!