Every time I have needed stickered, which has been very, very rare for carrier changes, they have done it on the spot. Usually, the carrier just took the ticket and moved on. The two stickers out of 20 or 25 changed carriers were on AY (only flew them once) and once on BA. I was told AY was common. It actually wasn't a change of carrier, it was an open ticket that they stickered to have a date when I checked in.