These are 3 liveries based on Lauda's Challenger 300. One of the versions is almost the same as the original except for the registration and Niki Lauda name on the tail (RIP).
Unzip the downloaded .zip file and copy the folder to the livery folder of your Challenger 300.
If you come across any issues, don't like something in particular, want something changed, added or want to have different registration write me on forum.x-plane.org or put it in the comments.
If you like my work, you can buy me a beer https://www.paypal.me/zenonstarcuk