Yep, you can freeze it! Freeze the pie before baking it and then bake it without defrosting it first. Also, because freezing causes fruit to release water (nerdy fact: when the water in the fruit freezes, the expansion of the frozen water causes the cell walls to burst) you need to use extra thickener to prevent the pie from being runny.
Another option would be to freeze the crust and the filling separately. Then when you want to bake the pie, defrost the filling and pour it directly into the frozen shell and bake.
Wrap frozen pies or crusts in foil and then store in freezer bags.
Yum! Blackberries are one of the things I miss about the NW!