I discussed my recent IRROPS situation with CO at "
Better CO IRROPS Handling - A Change We'll Like?"
Channa is spot-on, I'd only add that you should know ALL your options for alternate travel in case there is an IRROPS situation. Many of the GAs and reservation agents don't know anything other than CO or UA flights so know your options and it makes their life easier in an IRROPS situation.