The answer to my post just above is "yes", you can change your ticket, even if you have checked in. I arrived much earlier into LGW than expected (with VS), went to the easyJet "Customer Service" counter (for there is no such thing as a ticket desk) and in less than 10 minutes was my ticket changed to an earlier service at no cost and I was on my way. I cannot praise highly enough this Flexifare concept, it really bailed me out this Sunday, at real low cost compared the price of a normal flexible ticket.
The only thing was, the agent had no idea what a Flexifare ticket was and had never seen one, and was going to charge me for the change. Fortunately, there was a more experienced agent there who took care of it. So, you need to insist and say that you booked a Flexifare, otherwise they might think it is a normal easyJet ticket. Still good service, though.