[widespace_]

>Very easy if you have an Android phone Very easy if you have an Android phone from the correct manufacturer that and it's popular enough to have custom roms for it or you know how to port custom roms to other devices*

[phh]

Nope, nowadays any recent-ish Android can receive custom ROM very easily, using GSI.

But the restriction is that many OEMs and/or carriers forbids bootloader unlock.