Ok, I made the call this evening, followed the computer prompts, waited almost an hour for them to call me back, and got a friendly agent who seemed very agreeable to doing whatever I wanted on whatever days I wanted. Actually he seemed exhausted so I tried to take it easy on him. When I play this game, I use a mixture of pretending to know what I'm doing and I'm clueless and in need of help, and that's probably not far from the truth.
He said he could not change my airports from Cozumel to Cancun tho! I politely objected that they don't have same-day itineraries from CZM to LBB, but they do from CUN, and I really thought that they could make the change. I know at times in the last 19 years that some airlines have done it anyway as well as done it to me, Continental for one when I was escaping Hurrican Dean - gawd I miss that airline, but anyway - he couldn't, but he could ask for permission. Okee dokee, I'll hold. So I booked these flights illustrated below okay, and there was not even a hint of charging me more than the $286 I currently have in the ticket. I did opt for the 1½ hour connection in DFW which is foolhardy perhaps, but I'm going to try as I would hate to sit out that 4¼ hour layover for the later flight. If I miss my connection, then I'll try for the later plane. It'd be great to get back to Lubbock before 6 pm instead of my usual midnight arrival followed by my long drive home.
I do hope that there is an 8 am ferry departure that morning as I'll need that and a 9 am private van to make a 10:10 am check-in. The current ferry schedule shows a change to a 9 am departure being the earliest which would ruin this plan, but the whole industry is in chaos so who knows what's next. Now to email my trip insurance company.