You can acheieve this by creating a new instance of the event.
var _e:MyCustEvent = new MyCustEvent();
//do your work
//you want to remove the preventdefault
_e = new MyCustEvent. //store the data of the MyCustEvent in another objerct.
//Now after creating the new event, copy the event data to the new _e.
Mark as answer if this is correct
Post the sample code depicting your problem...?