Here is the module
I installed it on my S4 and successfully remapped the following key-strokes to lauch specific apps:
double-tap menu (a small glitch – it launches the custom app but also pulls up the menu of whatever or launcher is open at the time I double tap)
I realize there are loads of gesture launchers to get to things quickly, but some of these key remappings could be valuable to me also. In particular sometimes I find myself outside in bright sunlight with auto brightness disabled and can’t even see my phone to get brightness adjusted. Now I have mapped long-press menu to launch a Tasker-created app that turns brightness to max (and turns off autobrightness so I am guaranteed the phone will stay on max brightness after I press this button).
I also have Wanam installed. It didn't seem to work in changing button behavior. It does demand a setting for long-press home. I wondered if there might be a conflict. In Wanam I set long-press home to do “nothing” and in Xbutton I set a custom app… it followed the Xbutton instructions just fine.
There are some other features available also, but I haven’t tried them.
Sometimes the Xbutton App itself crashes when I am adjusting the settings of it. But it hasn’t caused any problems once it is set up.
Some people complained in the linked thread that after defining a button behavior (in particular long-press home), they couldn't set it back to default behavior. I think I saw that with long-press also. But I actually don't use the built-in behavior of long-press home myself (I have created a swype-pad action to pull up recent apps)
Thanks to the author of linked thread ( xperiacle ) who extracted this functional from Gravity Box and adapted it to work on Galaxy Note (and also GS4)