hi guys have an s4 in the uk im bored of stock touchwiz an want to install a custom rom. can i do this even tho its locked to 3? or do i have to unlock 1st? or does it not matter cheers guys?
Yes you can, you can change officially via Odin or install custom recovery and flash whatever rom you desire. I got my S4 back last year on o2 then flashed the BTU (unbranded UK version straight away) and now run the Google Edition rom. However I am on the bootloader and can flash whatever I wish without tripping KNOX but only via CWM.
KNOX when tripped can cause issues with warranty. Now as we live in the UK we have warranty covered for 2 years by the EU. But it's like a warranty flag they could use that against you and not fix any issues, it will also disable KNOX which is a security feature but more for commercial rather than personal and it you will not be able to downgrade your firmware.
You'll be able to go back to whatever stock rom you were originally on or higher. I suggest looking in the android development section for the pre rooted roms, I think there are ways to flash a custom rooted rom without recovery without tripping the knox flag.
ahh so its better if i just flash a pre rooted rom then?
so u think its better if i dont flash any recoverys but then how do i flash the rom over odin or?