Substitution of Noncommercial Message. Subject to the owner's consent, a noncommercial message of any type may be substituted for all or part of the commercial or noncommercial message on any sign allowed pursuant to this chapter. Design criteria which may apply to commercial signs, such as color, lettering style or height, and compatibility with other signs on the same parcel or other signs subject to a sign program, do not apply to noncommercial signs even when they are in an area subject to a sign program, master plan or specific plan. No special or additional permit is required to substitute a non-commercial message for any other message on an allowable sign, provided the sign is already permitted or exempt from the permit requirement. When a non-commercial message is substituted for any other message, the sign is still subject to the same location and structure regulations, such as size, height, illumination, duration of display, building and electrical code requirements, as would apply if the sign were used to display a commercial message or some other non-commercial message. This substitution provision shall prevail over any other provision to the contrary, whether more specific or not, in this chapter and applies retroactively to sign programs, master plans and specific plans which were adopted or approved before this chapter was enacted.