No, the size of spot/spill is controlled by the shape / size of the reflector, it’s not like a projector where you could simply reduce the apparent size with an apature (what your technically asking if you can do with the PVC).
In order to change the beam pattern on that light you can change to a different LED with a different size LES (light emitting surface) or you can just do what us guys here would do and get another flashlight more suited to your needs.