Changing Selection Texts

Is it possible to change the selection texts of the select-options while displaying on the selection screen.

Depending on one of the field values(pr_pt) on the screen.

I need to display different selection texts for the two select-options( so_usfd1, so_usfd2) on the screen, say,

1.) If (pr_pt) = A, then (so_usfd1) should b seen on screen as 'Water' and (so_usfd2) should b seen on screen as 'Oil'.

2.) If (pr_pt) = B, then (so_usfd1) should b seen on screen as 'Fat' and (so_usfd2) should b seen on screen as 'Color'.

Plz help.