general mods on air filter, LTA wun even bat an eyelid, unless u
go and slap a supercharger on after ur air filter. 
the muffler is part of the exhaust system, so its often
interchangeably referred to one another. change that, and u need to
get an LTA approved system. as long as not LTA approved, its
illegal to change to dat.
y does LTA keep tight tabs on exhaust, but are more liberal with
air filters? coz exhaust affects noise level and emissions, and
therefore requires sanctioning from their respective manufacturers
before its approved for use on the road. so dun be surprised, the
road legal exhausts are usually quite quiet.
so does the air filter or exhaust contribute to the noise? go
figure. 
