YEs - both the town office and the airport ticketing desk of CX are very good at handling OWE type tickets.

However, they are less happy to handle those issued on BA stock. I have used the BA ticket desk at the airport and the in town ticket office (shared with Qantas) and they have both also been excellent. The advantage of using the Qantas side of the shared office (in Jardine House) is that they don't try to charge you the BA GBP25 "do anything" fee in addition to the USD75 change fee for the ticket.