Just yesterday I changed a CO.com reservation from a deeply discounted IAH/BOS roundtrip to full Y IAH/SFO and SFO/BOS legs, keeping my I-class fare on the return IAH/BOS leg. The add-on was over $1400, including a $100change fee. Since converting a two-leg to three legs cannot be done on-line, I worked this through a telephone agent. Even though I was buying two full-Y legs, I could not convince the agent to waive the change fee (fair enough--I didn't argue the point). When I received my e-mail intinerary confirmation, I saw that I had a disconnect with the telephone agent and had been booked for an 11 am flight rather than an 11 pm flight on one of the Y legs. Calling up CO.com again, I explained the misunderstanding and was to be charged another $100 change fee, even though I was changing only one of the Y legs. The very nice telephone rep eventually waived the additional $100 fee, but I was a little surprised that the fee was applicable to a change to Y legs. Perhaps the change fee applies if there is a restricted leg anywhere in your fare?