Officially, no.

Officially, these seats are held for ATO (airport) assignment.

Officially, there is no "middle seat blocking" on CO like on UA or AA.

Unofficially, you will find many "elite line" agents who do give exit row seating to elite members. But many follow the rules and do not. Also, it is often possible to get these seats way in advance at the airport, especially at P Clubs, if you show an elite card. The rationale for holding for the airport is that they want to see that you are "fit" under FAA standards to be exit row seated; thus, it comports with this rationale to examine you before the day of flight for such an evaluation.

You will find agents vary as to whether or not they will assign in advance. I have often had agents do it and say things like "now, just don't go breaking your leg in the next six weeks!" etc.