Yes, you can. Currently, at its startup, the program browses the Sound folder and randomly selects .wav files for different voice calls. I mean if there are more than one similar files, like RogerBall1, RogerBall2 etc., it randomly selects RogerBall3, for example. Just keep your new files reasonably short (about 1 sec) and follow my 'naming convention', i.e. NameX.wav where X is a consecutive number. By the way, the Name part is hardcoded.
Are you going to add some new wavs or edit the existing ones?