In Maya 4.5 at least they fonts do have a history and this functionality might have existed in earlier versions also. Try the following:
In a new session of Maya 4.5 do the following:
1) Create>Text option box.
2) Reset all the options to the defaults: Edit>Reset Defaults.
3) Click Create
In the script editor notice that the MEL command that built the text looks like this:
textCurves -ch 0 -f "Times New Roman|h-13|w400|c0" -t "Maya";
In order to turn on history for the text object change the -ch 0 flag. The -ch flag is the state of the history of an object. It can not be changed once an object exists and can only be set before the object is created. Unfortunately there is not an option to enable this in the option box interface. You have to build your text from a MEL command and not the UI.
Change the -ch 0 flag to -ch 1 as in the following:
1) First delete your original text:
2) Now type the following:
textCurves -ch 1 -f "Times New Roman|h-13|w400|c0" -t "Maya";
3) Your text now has history. You can get at the history node by selecting one of the individual letters like the M in the word "Maya".
4) Open up the attribute editor and select the makeTextCurves1 tab. In the Text Curves History section should be a box called text that contains the text that is your string. Changing the text in this box will change your 3d text.
The font box is for informational purposes only. You can change the font but you need to do it with MEL
To change the font using MEL Use the setAttr command.
1) setAttr -type "string" makeTextCurves1.font "Arial Rounded MT Bold|h-13|w700|c0";
NOTE: Changing the font family is easy once you have a list of fonts installed on your system. Changing the text string however is problematic. Maya translates each curve by a certain amount. In the original example the lowercase "a" in Maya needs two curves to make that letter. If your new text doesn't just happen to have two curves in it also for its 2nd letter you will end up with curves offset from each other in an unusable fashion.
I hope this helps.