I spend far too much time on the ticket page praying for miracles but I've also done something like you want.
If you want to keep your current tickets as well as get new ones, as already mentioned, you'll need to be linked to other members and buy the new tickets on their behalf.
If you want to replace the tickets you already have and it's during TO hours you can get the new ones in your basket, give them a call and they'll help you swap them over. If you're on hold for more than 15 minutes you can click for more time to complete your order.
If the TO isn't open you'd have to be able to buy them on behalf of members you're linked to. If you then call later I think they'd still be happy to switch the names and cancel the others. I don't think you can do any of this too close to the game as they have a cut off.