HTC ONE build.prop

Hi all, I managed to get my phone unlocked with a code I got from the net

I'm now using my phone in the UK with ee UK Sims card

I have in my home BT broadband and can get free WiFi from various bt hot spots, problem is when I try download the app I get the message :

"not available in your country"

I have read something about build.prop and I really don't understand it, how easy is this to do and what's needed

Thanks