How do you transfer a minecraft world onto another account on a mac?

Just network them together and transfer the files.

Hook them to your home network or hook them directly via ethernet or wireless, turn on File Sharing and you should be good to go.

If you need more info click on the empty desktop and at the top of the screen click on the Help menu and type in File Sharing and or networking two computers. (You may need to be online for the Help menu to work)