As noted in your other questions, yes, you can ask for anything you want. However, from what I've seen on Avis lots across the country, I'd say you're most likely to get a Versa or Focus. If it has decent trim, a Focus is a great car and I've taken the Titanium Focus over much more "luxurious" cars.

However, unless you're a Chairman, calling/emailing/sending a message/faxing/sending smoke signals won't get them to bring in a specific vehicle for you. That's why the reservations say "or similar". And preferring an SUV on a compact rental is quite crazy. If you want/expect something like an SUV, you need to book it.

And you can go to the airport to switch-out. However, they will most likely put you in what you booked, as they're not making much/anything from a swap.