Hi,
do mDoc.changeGrep() twice.
1. for remove last character if ";", ":" or "." (and unwanted space by the way)
2. for add "." to every end of bullet's para.
so:
var myDoc = app.activeDocument;
app.findGrepPreferences = app.changeGrepPreferences = null;
app.findGrepPreferences.bulletsAndNumberingListType = ListType.BULLET_LIST;
app.findGrepPreferences.findWhat = "[\\.;:]\\s*$";
myDoc.changeGrep();
app.findGrepPreferences.findWhat = "(.)$";
app.changeGrepPreferences.changeTo = "$1.";
myDoc.changeGrep();
app.findGrepPreferences = app.changeGrepPreferences = null;
Jarek