Where in any parish, parochial district or area as defined by the General Assembly, or by any body to which the General Assembly may have delegated or may hereafter delegate the necessary powers, there are two or more separate churches or benefices, it shall be competent for the General Assembly to declare that such one of the churches within the parish, district or area concerned as the General Assembly may specify shall be deemed to be the church of the parish, and that- the minister and elders or kirk session of such church shall be deemed to be the minister and elders or kirk session thereof for the purposes of any Act, Act of Sederunt, trust deed, scheme of administration or other public or private instrument, deed or document having reference to the minister or to the elders or to the kirk session (as the case may be) of the parish as trustee or trustees ex officio, and, where the General Assembly shall have so declared, the church so specified shall be deemed to be the church and the minister and elders or the kirk session thereof for the time being shall be deemed to be the minister and elders or kirk session (as the case may be) for the purposes aforesaid.