Except as otherwise provided in this part, the Legislature may amend this part, by statute passed in each house of the Legislature by rollcall vote entered in the journal, four-fifths of the membership concurring, if the statute is consistent with, and furthers the purposes of, this part. No changes shall be made in the way in which funds are allocated pursuant to Chapter 3 (commencing with Section 99620), except pursuant to Section 99684.