Changing exisisting px4 drones to match own 3D drone model

I currently have a .stp file for an existing drone model that I would like to simulate by using Gazebo/QGroundControl.
I know that you can convert an .stp file into a mesh for simple appearances for gazebo, but is there a way to alter any existing default PX4 models to match my own drone?

Thanks for any guidance or assistance.