How to assign my home button function to a custom launcher? I installed Apex Launcher on my S3. It takes some configuring before it is useful, so I didn't assign it to the default action of my home key. I then did accidently set the default action to use the standard launcher.

I can't find any way to now set the Apex shell/launcher/what ever it is to be the default when you press home. 

Any ideas how to change my home button function?
Go to Settings > Apps > Click on the "All" tab then find your current launcher (the one that is default now) in the list. In the App Info page you should have the option to "clear defaults". Click this and the next time you hit the home button you will have the option to select a different launcher.