Tank,
If you are serving to the public there are rules to follow. You need to establish special, approved, procedures if you are serving at lower then recommended temps to the general public. I believe each state has it's own rules but you can be sure that they closely follow USDA. You have a lot more latitude if serving to family and friends.
Remember that the cleaner and safer the meat before you prepare it the better chance you have of producing safe food for your family. There is a time vs temp scale for food safety. In other words, you can generally cook to a lower temp if you keep the product at that temp for a longer period of time.
Generally if it's a quick cook item like burgers they need to be brought to a higher temperature. Burgers are particularly dangerous because of the grinding and mixing of different cuts of meat and the amount of food surface exposed to possible infection. Whole cuts of meat can generally be cooked to a lower temperature because if properly handled there is less risk of the meat carrying the bad bugs. I would think that if you buy whole cuts, grind them at home, using proper food safety guidelines (keeping the meat cool and work surfaces clean) and cook it right away, you can serve your burgers at a lower temperature.
Chicken and other poultry are a different story. Kind of like teaching in a kindergarten. No matter how careful you are you will still be carrying the bad bugs home with you. The overriding advice I have gotten from my readings is to always cook fowl to the safe recommended temperatures and clean all work surfaces and utensils with a disinfectant.
Most people that contribute reliable information to this forum can be more flexible in final cooking temperatures because they have taken steps to insure the safety of the product they begin with.
Pm me if you want me to try and find the pdf files of the guidelines, I think they are still on a disk somewhere.
Al