On your xplane toolbar, if you click on Challenger 650, the drop down menu will show you several tab, the first one is called "Airframe manager". Click on it, and you'll be able to create your own aircraft : you can select one of the liveries (which, by default, are made without any reg' number), modify your preferences for that particular aircraft, and put your own reg number on the plane.
It's very easy and intuitive, the best thing is to try
Hot Start - Challenger 650 - Jetflite livery
in Hot Start Challenger 650
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On your xplane toolbar, if you click on Challenger 650, the drop down menu will show you several tab, the first one is called "Airframe manager". Click on it, and you'll be able to create your own aircraft : you can select one of the liveries (which, by default, are made without any reg' number), modify your preferences for that particular aircraft, and put your own reg number on the plane.
It's very easy and intuitive, the best thing is to try