I did lots of date changes by just calling the airline or the TA - anybody who has access to your PNR.
And you don't need a sticker. As long as your reservation is changed you have your seat. Sometimes the airline sends you to the ticket counter to change the date on the ticket, sometimes they just accept the coupon with the different date. Never figured out when they require what.
But doint this at the airport is easy and fast.
So don't worry about stickers. Never had one before i went to the airport and never had a problem - i usually have a few date changes on my RTW's and i am doing around 3 a year.