I was just curious if this could be done and apparently it can so I'm just sharing the apk here.
It basically does what the title says, it enables multiple users on the Samsung I9300.
This apk was made from the latest nightly build of CM10.1 for the I9300.
I have updated framework-res.apk using the 2013/01/18 nightly build of CM10.1
Changed ROM to ParanoidAndroid. framework-res.apk
Changing the theme will cause the phone to crash when switching users. Reason unknown.
I have created a flashable zip file that works with ClockWorkMod, though its untested as I haven't had time.
I have also uploaded new screenshots. Another update will be coming soon with an updated CM10.1
I have updated the framework-res.apk using the CM10.1 nightly build.
With this update comes a restyled Lockscreen that will look nicer.
You may notice that it also doesn't interfere with widgets anymore.
PLEASE NOTE: This mod only works on Android 4.2 and higher! This mod has only been tested on Cyanogenmod 10.1!