I want to extend my stay, what is the policy around this? Can I book a deferred flight?

Yes, you may extend your stay. Make sure your itinerary booked in Egencia is within reasonable range of the flight you would've originally taken just for the work event (<10% variance). You should alert your approver of your desired travel itinerary. If you have an unusual case you would like the travel team to review, please open a ticket here.