I`m going to take a stab and say this doesn`t appear possible, but asking anywhow.
I have different events listed, but can I substitute a different button for the events. For some Id like to have it say `register^ and for others it to say ^purchase^ . I can edit the png file using fireworks, though I`m having trouble narrowing down the type font and font size.
You can of course modify the buttons however you want. The package comes with a zip file containing blank buttons with no text in each of the colors. Use those to make your own. Font sizes, etc are totally your call. You can even create your own buttons completely custom... even different sizes from the original. Just keep the same file names and you'll be fine.
HOWEVER... you can not make a new "Register" button that says something different per event. Whatever your register button says... that is what it will say for every event.