Thanks for the suggestion!
In FediMeteo we rely on the location identifiers provided by the Open-Meteo API.
For this specific location, the API uses "Londonderry" as the canonical name, and we currently follow that identifier to avoid ambiguity and mismatches in the data.
For this reason, the username cannot be changed, as it is tied to the Open-Meteo API identifier.
I have updated the display name and description to reflect both names. Due to caching, the previous setup may still be visible, but the updated description should appear within a few hours.
This is a technical choice rather than an editorial one.