Need to add switches to installer

[Pharaoh Atem]

I need to add a switch to an installer that will write a DIFFERENT INI setting instead of the normal one, using MUI.. How do I go about doing this? If it is easier to use InstallOptions to figure this out, then by all means do that!
The switch I want is "--user"
Code by default:

PHP Code:

WriteINIStr "$INSTDIR\\overrwdef.ini" "System" "OverWrite" "0 ; If enabled Program will use overwrite profile settings when run" 


Code I want optional:

PHP Code:

WriteINIStr "$INSTDIR\\overrwdef.ini" "System" "OverWrite" "1 ; If enabled Program will use overwrite profile settings when run" 


The code is in a section during file installation process, if you want to give InstallOptions thing, then it should be able to change within the section...