Wash. Rev. Code § 35.87A.140
Changes may be made in the rate or additional rate of special assessment as specified in the ordinance establishing the area, by ordinance adopted after a hearing before the legislative authority.
The legislative authority shall adopt a resolution of intention to change the rate or additional rate of special assessment at least fifteen days prior to the hearing required by this section. This resolution shall specify the proposed change and shall give the time and place of the hearing. Proceedings to change the rate or impose an additional rate of special assessments shall terminate if protest is made by businesses or multifamily residential or mixed-use projects in the proposed area which would pay a majority of the proposed increase or additional special assessments.
RCW 35.87A.140