Upvote:1
Usually no.
The travel agent owns the ticket until it releases it to the airline when check in opens. Until this point is not possible for the airline to modify the ticket. [The issuing airline can prematurely take ownership of the ticket in some cases, but they won't do this unless they really have to.]
The travel agent should apply the change fee and the fare difference that the airline stipulates; i.e., the same price should apply as did apply when going directly to the airline. However, the travel agent may also apply a service fee.