Greetings,
Exhaust noise is created as we know by the speed of the gases exiting from the outlet port of the exhaust system, so if the gases can be slowed down then the noise should reduce accordingly. However this can have a knock on effect to the fueling with consequential loss of torque or power as the slowing down at the exit ripples back to the cylinder head exhaust port and exhaust gas exit swirl velocity.
I don't know your particular bike so I do not know the exhaust which is fitted, however it might be possible to make and slide an extra baffle into the inlet side of the silencer. It might accept some simple stainless steel kitchen scouring pads (non soap type), or braze a few separated washers together to form a tube with say one inch gaps between washers, I think that you might get the idea
All very Heath Robinson I know but that is how my friends and I used to make our own silencers back in the sixties.
If the exhaust exit is too large then engine pick up and low to mid range road speed acceleration might be compromised, it used to be called exhaust 'megaphonisis' and sidecar Manx Norton riders in particular used to cover the exit with their foot (I kid you not)
Perhaps take a look at the videos on this link for some ideas;
https://www.youtube.com/watch?v=RNxKO18I-3Ihttps://www.youtube.com/watch?v=ld60v79wTDYLet us know how you get on.
TTFN
Hugh.