If you have an exit seat with an empty seat next to you it's a no brainer, especially on a redeye flight where there is essentially no service up front. And the first row in F on the 737s has such tight legroom that I'd probably opt to stay in Y even on a day flight (again, if the seat next to me were empty).

How to prevent being upgraded to row 1 is tricky. I would guess most GAs will get irritated with a complicated request like "if you're going to upgrade me but the only seat you have available is in row 1 then please don't". Most likely she'll just drop you from the upgrade list completely and move on.

Trying to swap with whoever lands in your original exit seat will be perceived as odd and could result in an extended conversation that no one is interested in that late at night.