|No offense, but wouldn't replacing single letters with a string of text make Word pretty useless. How would it know when you wanted to replace A with the above text or when you are beginning a scentence with A?|
There are two possible solutions. One is with shortcut keys - which I don't remember hot to do at the moment. But it would involve assigning a key combination to your desired text. Such as Alt-A, Alt-B, etc.
The other solution, which would be my preference is to create custom auto-correct options. The auto-correct function is used to automatically replace certain text with corrected text; such as misspellings [recieve->receive] and symbols [(r)->®]. You could set it up so whenever you type A1 (or something else that you would never use in comon documents) it would replace it with the desired text. You can access this function from the Tools<AutoCorrect Options menu.