Haven't checked this out myself and may be wrong, but there may have been some discussion about this before if you want to search the ROG forums (which I may try to do and edit this post later) for older articles about it, but sounds like Gps3dx provided some information about this (for older models?) with help from others in post # 45 below if you want to look into it more.
https://rog.asus.com/forum/showthread.php?56496-G751-How-to-change-the-Steam-Shadowplay-buttons-and-...
It links to another page below as well.
https://rog.asus.com/forum/showthread.php?87213-HOW-TO-REMAP-FN-KEY-and-special-buttons-quot-Steam-q...
Otherwise, one very poor workaround I found was using the Macro keys M1-M5 in the top left area above your keyboard.
Open the Macro Key utility and change the setting for a macro key from 'Launch App' to 'Set Macro' and record the key combinations you want to assign to that macro key.
Unfortunately, it doesn't seem to be able to record Fn+key combinations, so I need to use a bunch of extra key inputs to change the volume settings.
If you want to try it, record these keystrokes to lower the volume: (click on the record button for the macro key you choose), (Windows key+s to open/enter the search bar), (type 'vol' then enter key to open the volume settings), (press the down arrow one or more times depending how much you want to lower the volume with each macro key key stroke), (press 'alt+f4' to close the volume settings window) and stop the recording, save or apply the macro key and test it out.
The problem with this approach is that it should only work when you are at the Windows desktop, so be careful if you are in a game or other application and you actually need to watch and wait for Windows to perform all those steps (there is an option to change the keypress delays and speed it up some although to short of a delay will cause problems too), so you probably want to raise or lower the more than one setting per macro key press.
Expect there are much better solutions out there, so hopefully we can get more feedback, but just wanted to throw this idea out there to get the discussion started. Thanks.
