Change spoken words in text to speech?

In Navigator Free for Android, is it possible to change some of the spoken words in the text to speech?

Some examples:
Can I change  "carry on straight ahead" to "continue straight ahead"?
Can I change "slip road" to "exit"?
Can I change "roundabout" to "rotary"?

I've tried to edit the "navigation.xml" and "tts.xml" files but it doesn't change.  Does the TTS engine actually read and speak the printed text in these files or is the speech stored somewhere else? 

I read the questions and answers about "Direction change: say the distance at the beginning of the driving instruction" (http://forum.mapfactor.com/discussion/7002) but I can't seem to make changes.

Thanks!