I'm from the Fingerlakes Region of Western NY.
My situation may be a little different than yours because my GVWR was just under 26K, but I'll give you my experience.
First off, NY is a state where any vehicle with a registered weight over 26K needs a CDL with the exception of a RV. (House Coach is the term NY uses) Now, I said registered weight rather than GVWR because you get to define what your maximum weight is, so long as it is at or below the manufacturers GVWR and greater than actual curb weight. Meaning, if your bus has a GVWR of 33,000lbs, but a curb weight of 22,000lbs, you can register it as 22,000lbs and drive it legally with a class D licence.
Now, your officer friend is mistaken, on page 2 of NY MV-82 (Vehicle title and registration application) Section 4, line 3, is a field to note any changes made to convert vehicle class. This is how you do a title change in NY. You will fill out the first page with the desired vehicle class, and note the changes you made in this box.
That being said, there are changes which must be made to a school bus to make it no longer a school bus. NY VAT 375.21
Every motor vehicle having a seating capacity of more than seven
passengers, and used primarily to transport pupils or pupils and
teachers to and from school, shall be painted the color known as
"national school bus chrome."
In the event, however, such a motor vehicle so painted shall cease to
be used to transport pupils or pupils and teachers, the color of paint
herein provided for, shall be changed to another color, within fifteen
days of relicense.
It also stands tor reason that the special equipment required on school buses must also be removed, including flashing lights, stop signs and swing arms.
As far as what you want to register it as, and what you need in order to change it is up to you.
You have 3 real options:
1. Leave it as a bus (vehicle code BUS), wouldn't have to make any additonal equipment changes, but would require a CDL and a passenger endorsement. Probably not something you want to do.
2. Register it as a van (vehicle code VAN). In NY a van is a vehicle seating less than 16 people but more than 2, and able to carry both passengers and cargo. To register it as a van, all you have to do is remove most of the seats. One major benefit of this is that you only need regular private-commerical insurance, rather than School bus-RV conversion insurance, which can be hard to find. You also are exempt from parkway restrictions in NY as a van.
3. Register it as a house coach (vehicle code HOU). This is the most complicated one. According to VAT § 462.14
the term "house coach" shall
mean any vehicle motivated by a power connected therewith or propelled
by a power within itself, which is designed to provide temporary living
quarters, and which is built onto, as an integral part of, or is
permanently attached to a motor vehicle chassis, and contains at least
four of the following independent life support systems if each is
permanently installed and designed to be removed only for purposes of
repair or replacement and meets the standards of the American National
Standards Institute for recreation vehicles:
(a) a cooking facility with an on-board fuel source;
(b) a gas or electric refrigerator;
(c) a toilet with exterior evacuation;
(d) a heating or air conditioning system with an on-board power or
fuel source separate from the vehicle engine;
(e) a potable water supply system that includes at least a sink, a
faucet and a water tank with an exterior service supply connection; and
(f) a 110-125 volt electric power supply.
This is what you have to follow to be an RV. Up to you as to if its worthwhile to do. One benefit of being an RV legally is you become a residence, meaning a police officer now needs an actual search warrant to search the vehicle.
The vehicle code is what you would put in the "other" blank in section two of MV-82 under body type.
Personally, my vehicle is a 22,000lbs International Van, and will probably stay that way for the foreseeable future.
Let me know if you have any more questions!