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 a plan of unitization relates only to the rights and obligations as between working interest owners, the requirement that the same be approved by the owners of at least seventy-five percent (75%) of the production or proceeds thereof that will be credited to interests which are free of costs, such as royalties, overriding royalties and production payments of the unit area shall have no application.