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.
Ur tezmireḍ ara ad tekkseḍ { -brand-short-name } d amsaɣ-inek amezwer deg { -brand-short-name }. Akken ad tarreḍ asnas nniḍen d amezwer, yessefk ad tferneḍ deg tnaka n 'Sbadu-t d amezwer'