Can’t plan to go over 14 hour duty period under any circumstances   

After accepting the flight then go over 14 hours whether part 91 or part 135 and FAA and Company say that for those legs 135 rules apply with Medcrew or not, if it's part of my regulrly scheduled duty period. Can I use part 91 weather for that leg though? What about IFR rules? that repo leg is not part 91 because you are still on duty as it's a directive of company and were not released from the duty period with the required 10 hours of rest.