Account settings > server settings click the advanced button. Select inbox for another account. Choose local folders.

Be prepared. The entire account will disappear from the folder pane after you do this and it will not copy any email anywhere. So if you have stuff in the inbox you want to see later, move it before you start.

Thanks Matt. It took a while to summon the courage, but then thought I would move my entire collection of folders, sub-folders and emails to Local Folders and then change the server settings... It worked! No emails lost :)