I don't know how to make an uninstallable cab (but I'm pretty sure for things like this you can't), but I do know how to restore the keyboard without a hard reset. Download the Diamond Keyboards zip here
http://forum.ppcgeeks.com/attachment...0&d=1237532353 and unzip. use the task manager included to kill SIPGT_app.exe then install the cab you want.
p.s. I tried the OEM last night and when I cooked it in there was no keyboard and when I hit the button to pop up the keyboard the screen just went white. I don't know if you have tested it yet, but just thought you should know.