No, you shouldn't have to re-apply. The only reason that you might have to do so would be if you had torrential downpours within a day or so of the application. Too much rain may wash the application away. A little bit of rain is OK.
I put on Scotts with the Halts crabgrass preventer about 2 weeks ago. Since then a lawn rolling service has come along and will roll my lawn for $25. I'd like to do it but am concerned rolling the lawn could harm the crabgrass preventer. The way I understand it, the Halts forms a thin layer on top of the ground to prevent crabgrass from sprouting (I don't mean to sound like the commercial!). I believe the bag even said not to disturb the grass as this could harm the Halts. Will rolling the lawn harm the Halts?