I have some additional information regarding the webcam and conversion to IR. Examination of the lens revealed a flat glass window. I think it is the IR filter. I have attached a photo taken from my stereo microscope showing the reflection off the surface of the filter:
Also, examination of the back of the lens assembly revealed an odd lens. It is not smoothly convex -- the central portion is lower than the middle (it becomes concave). I tried taking a photo of the feature but it's not easy to capture. The strongest indication of this is a ring of scratches at the high point of the lens. Here's a photo showing what I'm talking about:
The ring of scratches can be seen just outside the reflections of the LED ring illuminator. I also confirmed that the central portion was lower by focusing back and forth between the center and high point.
I also did some measurements using a digital caliper to determine if the IR filter could be accessed by milling or drilling a hole in the lens body. The lens assembly screws into a molded piece that is mounted on the camera board. The overall length of the lens assembly is 18mm, and the IR filter is located 13.33mm below the front edge of the lens assembly. This places the filter 4.67mm from the back side of the assembly, smack in the middle of the threads used to mount the lens to the board.
I could be wrong, but I think the lens (with its concave/convex surface profile) probably is defective. I've never seen a camera lens with this configuration. A mix of positive and negative FL lenses, yes, but not BOTH on a common surface!
This, plus the fact that removing the IR filter would likely make it difficult or impossible to screw the assembly back onto the board, prompted me to find a replacement lens assembly. I found one with a 4.5mm lens, IR-ready, on ebay for less than $20. The lens mount appears to be a very common size -- 12mm diameter with .5mm threads -- so there are many choices available. I may have to modify the camera case to accommodate the replacement lens, but that is relatively straightforward if one has a lathe or mill (I have both).