Not a chance in hell a single exit with decats will pass any static noise test, let alone 96db, even with decats and std muffler you wil struggle.
I kept getting noise boards at Bedford (which means on the limit) of their drive by and that was with a true dual and hfc's, i know Bedford is one of the strictest but at least it gives you an idea.
Imho, swap out the exhaust, leave the std cats and you will be fine pretty much anywhere, 20 bhp "possible" gain from decats on a 1.5 ton is hardly worth the worry.
If you want to go faster on track, your 1 - 3 priorities should be:
Tyres
Brakes
Suspension
P.s forget a custom built exhaust, just buy a Milltek