Aer Lingus fee plus possible airfare.com admin fee plus possible difference in airfare, if there is

I booked a flight to Rome in May, but I realized I was a little impetuous and perhaps should have added a second leg to my trip. I booked my ticket on Kayak and I am flying with Aer Lingus . Unfortunately Kayak booked my ticket through airfare.com (which I know has a bad reputation), las vegas exotic car rental I called Aer Lingus and they assured me everything is ok with my ticket. I also inquired about changing my ticket and they informed me that I would only have to change their fees, I didn't mention airfare.com to the Aer Lingus operator. My question is will I have to pay both the Aer Lingus and airfare.com change fee or just one or the other.
Aer Lingus fee plus possible airfare.com admin fee plus possible difference in airfare, if there is one by adding a second leg. I assume airfare.com issued the original ticket, so would be the ones changing it and reissuing las vegas exotic car rental it?
Skybird is a consolidator - they buy blocks of tickets then resell them, to other agencies las vegas exotic car rental or to individuals. Nothing wrong with that; sometimes they are great deals. BUT It means that the AGENCY las vegas exotic car rental owns the ticket - and THEY set the rules for what the change fees are There may not be ANY way to change this ticket without buying a new ticket. Your best bet is to contact skybird directly.
As noted, Skybird is a consolidator. As such they often have change fees and other fees which may vary from an airline's provisions. Thus, airlines will not change a Skybird (or other) bulk ticket because the airline does not know what Skybird's terms of sale are.
Similarly, when a consolidator sells a bulk ticket las vegas exotic car rental through another agency (here, airfare.com ) that letter agency is able to do whatever they wish with those fees. So similarly, Skybird las vegas exotic car rental cannot change an airfare.com bulk ticket where fees are involved because they don't know what fees the customer was quoted.