Per FAA National Policy: "Part 91 operators are not required to comply with a manufacturer’s entire maintenance program; as such, overhauls are not mandatory for part 91 operators."**
Per FAA Chief Counsel: "Information not specifically referencing the design and configuration of an aircraft, such as ongoing maintenance requirements, is inappropriate and not binding on the owner/operator in a regulatory sense."
Per FAA National Policy regarding Part 135 operations: "Title 14 CFR part 135 (nine or fewer) requires compliance with at least the manufacturer’s recommended maintenance program. (Refer to part 135, § 135.421.)"
(All three of the above lines are from FAA Notice 8900.410)
** unless they are part of the Airworthiness Limitations for the aircraft.