I had read about how the filter - essentially a thick piece of glass, should be replaced to maintain the autofocus ability. Finding a replacement piece of glass the correct thickness isn't easy and dealing with optical companies is difficult and expensive for such a small piece of glass. I had thought of using microscope slides, the glass from photographic glass slide mounts or even an old filter (glass or optical acrylic). This involves cutting and layering the glass to the correct thickness.
This is too much work for something that may not be successful anyway. So this is what I did instead.....
Step 1: Open up your camera
I modified a FujiFilm MX2700. Looking at the reflected surface on one side of the glass showed that it appeared to have a yellowy reflective coating which was optically transparent when viewed straight-on. The other side looked like a normal optical coating. So why not just remove the IR reflective coating and place the glass back into the camera with a thin piece of dark filter to cut visible light and allow IR through?
Note that this is for the MX2700, your camera may have a different arrangement. The important thing is to find and remove the IR blocking coating once you've resigned yourself to modifying the camera and otherwise having to throw away the glass filter anyway.