That was a discussion between Paul and I.
He was the one that said they only last until the end of the event, but I've used them to fire in other events...implying that they stick around for a little while. I was going by the Help guide that said they last until the end of the game session. I haven't tried to verigy this.
You can make a temporary ASL that points to a different type of ASL -> b/c you can't use the ^ trick with other ASL types, but they last through the various game sessions, and the temp ASL could just look up the info again at the start of each session.