I recently booked a cash fare then within 24 hours, upfared and paid the diff by cc. A week later had an itinerary change come thru that I did not want, so chose to take the cash refund and I was refunded the entire amount including the upfare. Leads me to believe any upfare made within 24 hours would be fully refunded thereafter if still done within the original 24 hours OR schedule chg allows a full refund.