Or, you could just say "Numbers are for geeks" and go ahead and tow whatever you want...
I want to point out that I believe the quoted is said as tongue in cheek and for those that hear what they want to and ignore the rest. Do not believe this because it is what you want to hear.
There is no magic wand. Your rig is only capable of it's rating. As others have said, the engineers rated your rig because they know the limits of each component. Is your current hitch rated at 3.5K? Contact the mfgr and determine if your rig is capable of upgrading the hitch to 5K.
Please, please, please, Do not guess. Do not take a nonprofessional's or an anonymous source on a forum word for it It is not only your life and your families lives but those that travel on the same roads as you.