Mod Keys
 

Short question... Is it possible to have an onPress event know whether modifier keys (ctrl, alt, etc) were pressed during the click?

Not really. We can't see key presses of any sort really. Best thing we can see is maybe a textbox with an OnTextChanged event. Technically button events don't even have to come from the mouse nor can we tell if it has.

Well, that really is a shame :( I have to say, this UI "framework" we have to work in is really awkward and limited. Guess it was designed this way.

Yes. EQ2's UI is somewhat more locked down that certain other games of which we shall not speak. It's more secure in terms of possible avenues of exploitation. The Devs are usually pretty good about getting us the data that we need, within reason, but wide-scale modification of the actual framework of the UI isn't really doable.