I remember reading this several months ago, and thinking how clever it was. True, the whole hassle with changing the battery and having to remove a wire to reprogram is there, but depending on how many times a day to use the switch, the battery could potentially last for years.
Another way to approach it, if you had the ability to fish wires from that box, could have been to wire a standard (single-pole) wall switch to the contacts of a PowerFlash module, and locate that somewhere out of the way.
The PowerFlash is more expensive than a keychain remote, and they take up an outlet (which, if you have several of them, can be its own nightmare to deal with), but they never need battery replacements, and you don't need to deal with modifying anything.
I don't recall the different modes offhand, but there is a mode for a "momentary" contact, and for on/off, based on the status of the switch you wire to the contacts.
Several years ago, I read instructions on Ido Bartana's website (
www.idobartana.com) for modifying a plug-in "tabletop" controller to act as a contact-closure module (like a Powerflash), but with several sets of contacts.
It wasn't hard to do, and that could also be used for an application like this.
I'm not saying your approach is bad (in fact, I think it is brilliant!), just thinking of other ways to do the same thing.