A quick but not elegant solution is to use AutoCorrect under Tools. You can
set, e.g.,  \E to be replaced with É. While making your slides you would have
to type a space following the E in \E, as the space triggers the AutoCorrect.

Of course you need to add all your special characters to AutoCorrect. By the
way, you will need to paste your special diacritic characters to AutoCorrect
as you cannot insert them there, at least I do not know how to do this.

I have been thinking about a code to allow this type of things but run into
a roadblock: I do not know how to read a text being typed to PowerPoint in
real time, unless it is typed to a text box on a form. Any ideas? Steve?