I don't want to advocate flying over gross, but it's like many things, understand it and handle it properly and it can be fine. I've owned two airplanes that were certified at one weight, but approved to carry more weight if certain mods were made, but not legal unless an STC was complied with which was paper work and placards. So, if I fully understand what's going on, I'm technically illegal but within reasonable bounds.
On my current C90, I can get a 700 pound gross weight upgrade by putting on 10 ply tires and purchasing an STC from Beech for $16,000 which is paperwork and placards.