I tried this last year on an international->international connection which had no change fee and space available in the fare class I was in on the earlier flight.

Tried inside the lounge - sent me to lounge front counter.
Tried at the lounge front counter - sent me to the TK customer service desk.
Tried at the customer service desk - Sent me to the customer service desk in the arrivals area
Tried at the customer service desk in the arrivals area - Sent me to the lounge or the customer service desk in departures.

Eventually I gave up, paid the US$60 for a visa (which I needed on the return anyway), went through immigration, went to the ticket counter outside, paid a $25 service fee, and they changed me.

In doing so I missed the flight I wanted, but got another one an hour or two later.