• Copy the particle system to your project
• Locate the 'flash' particle effect within the copied system
• Adjust the 'phase' parameter to change the angle of the flash
• For more precise control, modify the Dimension Axis to Object X, Y, or Z. This will make the particle align with the rotation of the object that creates it.

Of course, check the Documentation section of this page.

Please un-zip the archive and open the .blend project.

No, it's a plugin that uses a .blend file that has all the assets, textures and logic (node groups) inside for direct use. You can copy any of them over to any of your projects, while also preserving their original functionality. Before use, un-zip the archive.