#Question: S4 I337M Virgin(bell) Need infos topic

So I Currently have an Xperia z and my girlfriend as A Galaxy S4 I337M , We plan of Switching phones between each others, But First I need some infos before making the Switch. I am Currently on a Rooted phone with Custom rom So I want to make sure that Once I switched to the S4 I will be able to do so I've hearded some S4 are bootloader locked and **** about knox.

So is there anyways to know if the phone will support root/flashing custom roms ?

Thank you