Is it possible to change the key of an audio recording. More to the point, I have a 40 track audio recording of a song in the key of E but I'd like to lower it to Eb.

If the tracks were recorded directly in Logic you can use "Transposition" in the Inspector. "Follow Tempo" needs to be checked for this to work. You can have mixed results with this so try it on one track before transposing you whole song! I think your best bet would be to get the final mix in a new project and try to transpose it using "Factory / Time and Pitch Machine" in the Sample Editor local menu.