Individual with a permanent physical disability who has lost all mobility that precludes locomotion without the use of a mechanical aid or prosthesis. Exemption, Form 458B (available from the county assessor), is required.A homeowners' exemption may also apply to a supplemental assessment. For more information, call (925) 313-7481. Disability for Homestead Exemption, Form 458B (available from the county assessor), is required. You must file the application (Form 458) with the county assessor's office where the original home resides between February 2 to June 30. STATEMENTS. This claim may be used to file for the Homeowners' Exemption for the Assessment Roll and the Supplemental Assessment Roll.