I'm getting a little confused by what you are saying. If I understand correctly, this is what you did? 1. Bought pack. 2. Made a flashlight in a 3d modeling program. 3. Brought the flashlight into fpsc as a weapon, with the flashlight script. 4. Attached the flashlight mesh to a dessert eagle mesh and brought that into fpsc.
If that is what you did, then no it will not work. However, (Id on't have the script so I'm not sure), if the flashlights work off of a script linked to in the FPE, then in theory you could make a regular gun, get it all working, then link the flashlight script into the new weapon's fpe. Of course, this is theoretical.
The quick brown fox jumps over the lazy dog