[how-to] remap genius key
1) Boot in to ClockworkMod Recovery
2) mount /system from partitions menu
3) adb pull /system/usr/keylayout/latte-keypad-v2.kl latte-keypad-v2.kl
4) Edit file locally, the genius key is: key 187 (make a backup of the original file first)
5) adb push latte-keypad-v2.kl /system/usr/keylayout/
For more information on remapping keys see: http://forum.xda-developers.com/showthread.php?t=695936
If you want the genius button remaped to ENDCALL (if on a call it will end the call, if not on a call it will lock the screen, if you hold it down it activates the power button menu) and don't won't to edit the file yourself you can download this premodified version, just place it in the directory you are running adb from and skip steps 3&4): http://www.4shared.com/file/ein06_25...keypad-v2.html
There is a slight hardware delay on the button press, so whatever you assign it to you need to hold the button for half a second just like with the current genius app.
It does not seem to be any easy task to be able to call an alternate application, for now, you can only reassign the key to something another key already does (letter/number, end call, power, volume, camera, etc.). I'm currently working on being able to call an alternate application.