As of January 1, 2005, marine law enforcement officials are using a safer and more efficient method to measure and enforce existing maximum noise levels for recreational motorboats.
No, the law only changes the method of testing noise levels, it does not change the relative decibel limits.
You should not need to replace your muffling system unless your boat was already out of compliance with the noise level limits before January 1, 2005.

However, the law now requires all vessels to have a muffling system that is in good working condition, is always operating, and brings the vessel into compliance with the noise limits. Most mufflers meet these requirements.
The older method of testing for motorboat noise was potentially dangerous and difficult for law enforcement officers to conduct because it required officers to set up a special testing course and run the boat full throttle through the course.
Recreational vessels that are competing in a permitted regatta, boat race, trial run or speed trials are exempted from the noise limits during the time and within the designated area authorized by the permit.
Several other changes also went into effect January 1, 2005:
The motorboat noise level laws became applicable to coastal waters out to one mile from the shore instead of just inland waterways.
The motorboat noise level laws became applicable to state registered recreational vessels and federally documented vessels used for recreational purposes, which were previously exempt from motorboat noise laws.
The boat owner became responsible for the boat’s noise level instead of the operator who may have borrowed or rented the boat because the owner is responsible for basic maintenance and operability of the vessel.
Harbors and Navigation Code Sections 654 – 654.06. (scroll down to section 654)