Whether or not you ask permission, I'd want to know if I were hurting my own system with the extra load. Your county will have a limit for your tank size. They usually go by number of bedrooms, fixtures or such to guesstimate the max load the system will have. The actual number of people on the system would be the most important thing, in your case. Also , bigger tanks will handle more. If you don't know the tank size, you can measure the depth and ask a tank builder. Then your codes will tell you how much house it can handle, in terms of fixtures, bedrooms etc.
FWIW, I had a 4 BR 1999 house in Az. And the code at the time it was built only called for a 1250 gal tank. I now have a 3 BR house in Co. and it took a 1500 gal tank... Codes change. In Az., I ask a county inspector about adding a rv dump to that 4 BR system with only two people in the house. He said, 'do it'. Craig