Properly Registering my Weight

I have a towing business in which I regularly travel across a provincial boundary (I live 10 miles from one). Initially, I registered my tow trucks at 25,997 lb. That number is very satisfactory for 95% of the work that I do. Both of my trucks GVWR are 26,000 lbs, yet GCWR are 40,000 lbs. I have a 20,000 lb trailer that I can pull behind the one truck for heavier loads. With the little research I've done, I understand that there are great benefits for me keeping my registered weights at 25,997 lbs, but I did not previously understand that pulling my trailer would affect my truck's registered weight. If I want to continue doing that extra 5% of the work (real gravy for me), do I have to increase my registered weight, or can a permit increase it when necessary? I'm sorry to ask such amateur things, I seem to learn new things every day.