You can prevent AutoCorrect from correcting specific abbreviations or words that have mixed capital letters and lowercase letters.
Choose \<emph\>Tools - AutoCorrect\</emph\>, and then click the \<emph\>Exceptions \</emph\>tab.
Do one of the following:
Type the abbreviation followed by a period in the \<emph\>Abbreviations (no subsequent capital) \</emph\>box and click \<emph\>New\</emph\>.
Type the word in the \<emph\>Words with TWo INitial CApitals \</emph\>box and click \<emph\>New\</emph\>.
To quickly undo an AutoCorrect replacement, press Command Ctrl+Z. This also adds the word or abbreviation that you typed to the AutoCorrect exceptions list.