With P3D 4.5 there is an option to reload shaders without exiting the simulator.

Simply bind the “Reload Shaders” control to a button of your choice. Then open up PTA or Tomato, change the setting you like and save / install the shaders.

Use your Reload Shaders button and watch simulator refresh the shaders. Screen will go blank for some seconds though.

Here is the location of the new control assignment