Take a look at system libraries/carrier bundles/ check which r ur default settings and which ones u need to change make a backup before doing any changes be very careful as I'm only telling you where u can find the info I r looking for hoping it helps u but I have not tried my self but I went throughout all those folders and files and the ones that r as default for my phone and i notice tha for each setting wifi,3G,LTE, for each setting in the plist there's a value and those r the values there in that folder well at least for my iPhone 7+ that's where they were first read and then before trying anything ask here in the forum and see if someone else can help us verify if changing any values would work as I'm also interested in this as well