It used to be the case that one was advised that Android installations were tweaked by the network operators to suit the radio aspects of their particular networks (not just the bands, but maybe drivers and some technical parameters).
 
Is that tweaking still the case or with the more comprehensive radio band capabilities of (many) modern handsets is that now not a consideration?

(The context for this question is the possibility of buying a particular handset which is not available from a NZ mobile operator, eg Sony XZ1 Compact)