Used code bought on internet to unlock Galaxy S3 from 3 UK to O2-UK. Will rooting the device harm it? My Galaxy S3 was locked to 3-UK when I got it.  So I used a code I bought on the internet to unlock it.  When buying the code the form asked which network I wanted to unlock the handset for.  I said O2-UK as that's the SIM I want to use.  No other SIM cards work on the handset except 3 and O2.  If I root my handset will O2-UK still work on it?  Thanks to anyone that can help.
Rooting the phone won't change SIM-lock settings, they're saved in a separate part of the phone, please see these previous questions for more info on that: Where are the SIM Lock settings stored on an Android phone?  and Does Unlocking bootloader affect network lock?

You can find more explaining these different terminologies here: What is the difference between: Rooting, Jailbreak, ROM, Mod, etc.?