The safest thing to do is run stock pipes so you never have to worry about it! Most track day hosts will not take any responsibility if you are black flagged and asked to leave. The sound meter is at turn 5 which is a left hander and leads up a hill towards the corkscrew. A lot of folks with aftermarket pipes simply short-shift at that turn to try and avoid getting flagged for sound. Laguna requires you to have a number on the front and right side of your bike so that the sound worker can report you to the host who will in turn ask you to correct the problem (usually get two warnings and then the third strike you're out)!
Again, easiest if you just go with stock exhaust but if you cannot, I've seen plenty of folks with aftermarket pipes have a great time at Laguna...it also depends on what pipe you have and what bike. Ducs are notorious for getting too loud even with stock exhaust.
Are you planning on going? I'll be there in March! Good luck!