Long story short, my company uses a travel agent to book tickets. I want add a stopover on the return flight (domestic) to see some friends and want to avoid the internal bureaucracy to get that approved (and pay the fare difference).

In the past when I have purchased tickets through this travel agent, it appears immediately in my mileageplus account. I have also been able to make changes to the reservation as I need by paying the change fee through the United website.

My question is can I make a change to the reservation and pay for any fare difference through United.com within 24 hours without having to pay the change fee?