Microsoft Flight Simulator X is not easy for making design changes in airplanes. There are third party airplanes that can be added but modifying the aircraft is not easy and typically not done by the average user.
Laminar research “X Plane” is a completely different story. It is made specifically for aircraft and performance modifications. You can easily change an instrument panel and the performance of the aircraft by running the “Plane Maker” program to customize your airplane for your specific instruments.