I've been going cross-eyed over the last few days, reading the CT motor vehicle statutes. So far, I haven't found anything to indicate any restrictions on Classic/Historical/Antique plates.
I did find that in the 14-1(17) definition section, they clearly indicate commercial registrations are for vehicles engaged in businesses. In 14-1(16), they also indicate that "Commercial Vehicle" is anything over 26,001 lbs, OR designed to carry 16 or more passengers, OR to transport 10 or more students under 21, OR transporting hazardous materials.
(16) “Commercial motor vehicle” means a vehicle designed or used to transport passengers or property, except a vehicle used for farming purposes in accordance with 49 CFR 383.3(d), fire fighting apparatus or an emergency vehicle, as defined in section 14-283, or a recreational vehicle in private use, which (A) has a gross vehicle weight rating of twenty-six thousand and one pounds or more, or a gross combination weight rating of twenty-six thousand and one pounds or more, inclusive of a towed unit or units with a gross vehicle weight rating of more than ten thousand pounds; (B) is designed to transport sixteen or more passengers, including the driver, or is designed to transport more than ten passengers, including the driver, and is used to transport students under the age of twenty-one years to and from school; or (C) is transporting hazardous materials and is required to be placarded in accordance with 49 CFR 172, Subpart F, as amended, or any quantity of a material listed as a select agent or toxin in 42 CFR Part 73;
14-1(17) “Commercial registration” means the type of registration required for any motor vehicle designed or used to transport merchandise, freight or persons in connection with any business enterprise...