Change ur name

I want to legally change my name to Ren (Ren is a derivative of my birth name, and I picked it b/c it's a phoneme that shows up in both male and female names. Unfortunately, living overseas means it would be a hassle to change my name, and then I'd have to either get a new passport remotely as well (expensive, bothersome) or submit a proof of name-change every time I want to use Ren anywhere (bothersome.) It probably won't happen until I get NZ citizenship, as such.