Amendments to the approved or conditionally approved tentative parcel map or conditions of approval shall be made in accordance with SMC 16.28.120, except that amendments which in the opinion of the Planning Director and City Engineer are not minor shall be processed in the same manner as the original tentative parcel map. Any approved amendment shall not alter the expiration date of the tentative parcel map unless an extension of such date is also specifically approved pursuant to the provisions of this chapter.