For various reasons being the most prominent the fact that in my country (Portugal) many services are still unavailable .. I was thinking of changing my phones firmware to UK's firmware. I just don't know if it is possible without messing knox or any other kind of problems.

Anyone here has enough experience and/or knowledge to know if this is possible? If so should it clean flash it? Or just dirty flash it?

NOTE: Although I have some experience with custom roms and odin.. the experience is from the time of my S4.. so I'm kind of rusty.

Thanks in advance to anyone who can help..