They are not permanent in any version of Word to my knowledge. That said, here is a link to a macro solution.

http://answers.microsoft.com/en-us/o...5-5bb0e6156645
Set the forum to display all replies and view the oldest first to make sense of this.

Here is a link to a template implementing this which can be used as an Add-In. I have no idea whether it will work on a Mac but it shouldn't hurt if it doesn't work. It works on my computer. To use it, you would put it in your Word Startup Folder. You need to download the template, not create a document based on it. The explanation of what it is doing is in the thread I linked.

https://www.dropbox.com/s/jg1xl19o9c...2013.dotm?dl=0

This is a temporary link.