Yes you can and you can switch bowling balls at any time during the game. Switching bowling balls is a good thing to do if you need to or the lane is starting to change. Over time the oil will start to be pushed up the lane or start to dry up and some bowlers will change bowling balls to something that can handle dryer lanes.
Maybe there is heavy oil on the lane and you may need to change to a stronger bowling ball. Yes you can switch bowling balls while bowling if you need to. The best thing that you can do is know the bowling ball that you are switching to and know how to ball rolls. If the bowling ball is not good with dry lanes, then I would not change to that ball.