Yes, you can enable all application on one of the great features in Samsung Galaxy S III Premium Suite Upgrade ~ Multi Window now. More and more Android 4.1.2 firmware is available for Samsung Galaxy S3 like XXELKC, XXELL4, XXELL5 and XXELLA. All of them support Multi Window but only few applications can be used in that mode. Luckily, you can enable all applications in Samsung Galaxy S3 Multi Window with the same mod from developer who developed for Samsung Galaxy Note 2. As usual, root access and CWM are required.
Unlimited apps in Samsung Galaxy S3 Multi Window
Use MultiWindow Complete Control Tool to add more applications in Samsung Galaxy S3 Multi Window. Just put the applications that you want and you are ready to go. You need to install framework hack with CWM first. And install MultiWindow Complete Control apk later.
Installation guide – How to install update zip with ClockworkMod Recovery on Samsung Galaxy S3? (Video)
Download MultiWindow Complete Control for Samsung Galaxy S3 here.