Make sure the title line (the first one) is different from the original one. If its the same as the original .cfg entry the sim will only see one of them.
[fltsim.0]
title=Cessna 337 Skymaster <--- this one
sim=c337
model=
panel=
sound=
texture=1
kb_checklists=c337
kb_reference=c337
atc_id=N778WS
ui_manufacturer=Cessna
ui_type=C337 Skymaster
ui_variation=White with green
description=Several years after production of the 182 ceased, Cessna brought it back as the S model. While a number of enhancements make it a step forward in development, the 182S retains the remarkable characteristics that have made the 182 a popular airplane: power, stability, and good load hauling capabilities. The Skylane 182S is an ideal airplane for pilot training. If you're new to flying, you'll find Rod Machado's flight lessons in the 182S very helpful. You'll find them in the Flight Simulator 2000 Pilot's Handbook. For enhanced instrument flight rules (IFR) panels, choose the 182S IFR. See the Aircraft Information section of Help for tips on flying this aircraft.
atc_heavy=0
atc_airline=
atc_flight_number=
Hope this helps
Chris