Add to your C:\Program Files\Microsoft Games\Microsoft Flight Simulator X\SimObjects\Airplanes\CS_B757-200F / Aircraft.cfg file

Replace "XX" with the next in the sequence.

[fltsim.XX]
title=Captain Sim 757-Freighter CaymanCargo
sim=cs757-FRR
model=RRW
panel=
sound=RR
texture=CAY
kb_checklists=
kb_reference=
atc_id=VPCCJ
atc_airline=Cayman
atc_flight_number=757
atc_heavy=1
ui_manufacturer=Boeing
ui_type=757-200 Freighter RR
ui_variation=Cay AirCargo
ui_typerole="Commercial Airliner"
ui_createdby="Captain Sim"
description='757 Freighter' Expansion Model v.4.2 FSX \n(c) 2008 Captain Sim \nwww.captainsim.com