I have found how to do it!
There is a file in the shipsim program files called "custom P6 read me". It tells you the files you have to edit to change the texture, one to change the icon and another to ajust the behavior (you can change the speed, engine positions, max turning angle and a whole lot more!).
It is definately worth a look and a play about/experiment.
(don't worry about changing the programming as the defults for the speed etc. are in the readme file for if you can't remember)
