How to modify possible values screen timeout on rooted devices? I've managed to root my device.
I wanted to keep my screen awake forever. However when I looked around the Settings, the maximum value is 1 hour in the Display settings. There's a 'never' in Developer settings, but only when device is being charged. I used Tasker to set the timeout to Never, but it gets changed back when I click the  Display Settings. I used Android wakelocks but they stop working when they're removed from the memory.

I know those settings are practical enough, but as a geek I would like to know how to get 'Never' appear in my Display Settings.

EDIT: To repeat again, I DO NOT want to use an app or a wakelock to accomplish this. I just would like to have my ROM (/system partition) modifed so that 'Screen timeout: Never' appears in my Settings.
In order to keep screen awake forever:


Download No Screen Off app and install it.
(Ignore this PLEASE) If you know android programming, you can use this snippet in your app: 


getWindow().addFlags(WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON);


Some phones have "Keep screen turned on" option in Screen timeout
settings.
(Requires Root) You can use PerApp for making change in Screen timeout
settings and add your own value.(customize)
There is a stay awake option in "Developer Options" to Stay awake
while USB debugging and charging.