It is not possible to unset { -brand-short-name } as the default client within { -brand-short-name }. To make another application the default you must use its 'Set as default' dialog.
Ní féidir { -brand-short-name } a dhíshocrú mar chliant réamhshocraithe taobh istigh de { -brand-short-name }. Chun feidhmchlár eile a roghnú, caithfidh tú an dialóg 'Socraigh mar réamhshocrú' san fheidhmchlár sin a úsáid.