14 CFR 135.101 isn't an "exception." It's the rule. If operated under IFR, the SIC is always required.

An exception may be made to 135.101, which is 135.105; if approved by the FAA, an operator may use an autopilot in lieu of a SIC, when operating under IFR. This is an exception to the SIC requirement of 135.101: if the operator maintains a SIC training program, the operator can fly without the autopilot, and use the SIC.

Using a SIC isn't a special exception to autopilot use. The FAA doesn't have a program for use of a SIC in lieu of the autopilot. It's the other way around. The SIC is basic required equipment, and an exception may be made, if granted authorization under the company Operations Specifications (OpSpecs--specific rules and authorizations granted to that operator by the FAA) to use an autopilot instead of a SIC. The operator does not need a special authorization to use the SIC instead of the autopilot, because the SIC is already required under the regulation.

If an operator flies single pilot with autopilot and does not have a training program for the SIC, and the autopilot is inoperative, then when it comes to IFR, the airplane can't be flown under IFR. It's important to understand that the second in command is a core requirement for passenger carrying operations under IFR. Autopilot operations are not.

This does not apply to cargo operations.