I don't really get what you're trying to do. The islands don't have names, except the internal ones like N_S01, but I doubt you want to change those. The names in the game aren't the names of the islands, but of the cities. If multiple players have buildings on the same island, then they have different names, too. As Jesus wrote, you can change the names of your own cities, but of course you can't normally change the names of cities that don't belong to you. And unsettled islands don't have cities, so they don't have names either.
Ach, und Jesus ist auch wieder da. Ich hab die Hoffnung nie aufgegeben, aber du hast meine Geduld ganz schön auf die Probe gestellt.
I just want to change the names of all settled islands...
For example, my main island could be England, van der Mark's main island could be Netherlands, while Helena Flores could be Portugal and so on. For the secondary islands I could explore the allies/colonies of those countries...