UK iPhone 1.1.2 Jailbroken

My phone is to be used in two countries, Uk & Greece

In the UK the phone works great with an o2 PAYG SIM which I am happy with. When I'm in Greece I am going to use an X-Sim so that I can use my Greek Vodafone PAYG SIM.

In iWorld I see the Greek setting but not UK.

My question is, when I install the Greek settings using iWorld do these settings overwrite the UK settings that are the default settings at the moment? If the settings are overwritten how can I change back to UK settings when I return home because UK settings do not appear in my version of iWorld.