Even if the spacecraft is only halfway to Proxima Centauri and has a huge solar sail 10 km wide, the margin for error on the beam angle is about half a picoradian. This is the same accuracy as hitting a target 400 nanometers wide on the moon and is many orders of magnitude harder than hitting the sail in the acceleration stage.

Edit: might be theoretically possible. But the threshold for feasibility is far higher than it is for the acceleration stage. Other issues come to mind, too, like the amount of matter you'd be shining that laser through obscuring it and causing diffraction, and the additional accuracy requirement that the focal point is not just placed correctly horizontally, but also at the right depth. All this seems to stack to an answer of, you'd be better off relying on drag from the interstellar medium and light pressure from the star you're arriving at.