The unit area of a unit may be enlarged to include adjoining portions of the same common source of supply, including the unit area of another unit, and a new unit created for the unitized management, operation and further development of such enlarged unit area, or the plan of unitization may be otherwise amended, all in the same manner, upon the same conditions and subject to the same limitations as herein provided with respect to the creation of a unit in the first instance, except, that where an amendment to plan of unitization relates only to the rights and obligations as between lessees the requirement that the same be signed, ratified or approved by royalty owners of record of not less than sixty-three percent (63%) of the unit area shall have no application.