I put in new batteries, and the remote came back to life. All the programming worked, and the light went out in 5 seconds after pushing a button, just as I programmed it to, in a vain attempt to compensate for the failed switch. The remote doesn't come on anymore when I pick it up, but it also doesn't stay on for days anymore either. I just push the "Glow" button to get the light now.
1. Remove the battery door and unscrew the 4, #0 Philips-head screws.
2. Separate the battery-case end of the remote from the front of the remote. Slide the two battery springs out of their slots in the battery case.
3. Separate the front and back case-halves until you see the first spot where they are held together by a plastic snap. Insert a thin screwdriver between the case halves and push in. The snap will spring back and the case will separate. Repeat on the opposite side.
4. Repeat step 3 until you have the case separated. There are 8 snaps holding the case together.
5. Pull the IR lens out from the LEDs and the USB connector.
6. Separate the case halves.
7. Look at the circuit board. Locate the switch, reference designator SW01. It is a relatively large, rectangular device, located just in front of the battery case, with two leads that are planar soldered to the PWB.
8. Unsolder SW01 from the PWB.
9. Re-assemble the remote.
I imagine this procedure works for the Harmony 550 as well. Don't do this if your Harmony is under warranty. Logitech will replace the remote for the lights-stuck-on failure, after they jerk you around for a while with tech support.