Mobile network settings - Not enabled for modifications (Greyed) I bought a zte v7275 tablet

Device information


model number - ZTE V7275    
android version - 4.0.4
kernel version- 3.0.21-perf-gc8726c4f
Flash ROM 


which is likely to be locked to a single operator (vodafone, but I haven't tried it with vodafone sim card). Any way when I insert a different sim card and navigate to "Mobile network settings" section, I can see all the operator network related configurations are disabled (greyed). I know this particular modle of device is rare in use. 

But I would like you to suggest best option I have, following are some of things I came up with 


Install ROM to 4.1 , assuming operator lock, will be flashed 
Install custom build Phone.apk for android 4.0.4 and repalce the existing  Phone.apk system app


Further can I know different stratergies can be used to disable the Mobile Network  Settings, so I can reverse it. 

Thanks
If your device is locked to Vodafone (as you write), a different ROM won't change that. You will either have to use a Vodafone SIM, or have the device unlocked from the provider.

I'd suggest you first try whether the problem persists with a Vodafone SIM, to make sure whether a SIM-lock is the cause. Those network settings are also grayed out if you've got no SIM inserted at all (I've tried that on one of my devices) – so it usually means you don't have those services available because there's no accepted SIM card detected.