I’d make it simpler and have all the materials that need such functionality use Material Parameter Collection in which you have an int ‘current flashlight’. Set that value in the MPC through code or blueprint when changing the flashlight.
Then in the material, normally react to light (make the text on normalmap or spec) but check for that int whether it matches what you need. Use lerp or switch, both would work. MPC is quite well documented, you should be able to get it up and running quickly.