If you are certified as a 107 pilot (you've taken and passed the test and paid the fees), the way I understand it is you put the 107 # on it and it is unique to that aircraft. It's your intent that causes the flight to be considered rec or 107 so your business aircraft would have the 107 registration # on it and you decide to fly rec (and that's your intent), your fine. I could be wrong as I've never taken the 107 test. As a rec flier I basically registered myself ($5) and all my airplanes, helicopters, and multirotors all have the same number on them.