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.
Chan urrainn dhut { -brand-short-name } a thoirt air falbh mar an cliant bunaiteach o bhroinn { -brand-short-name }. Ma tha thu ag iarraidh aplacaid eile mar bhun-roghainn, feumaidh tu a dhol ann is bun-roghainn a dhèanamh dheth o bhroinn fhèin.