In Blender, I already baked Rigid Body Physics for about 200 frames. Is it possible to continue baking, or do I need to Free Bake or Free all Bakes and start all over again?
What you should be able to do is 'Free Bake' but leave the baked frames in the memory cache (the frames in the timeline should switch to being marked in lighter orange instead of dark orange). Then play your animation (without changing anything about the objects which were previously baked) and Blender should play the 'cached' frames and then continue the animation from the point where the baked frames stopped. Once Blender has completed the simulation up to the new end point then click Current Cache to Bake to convert the cached frames back to a baked animation - without re-simulating.
Note, however, that you have to be very careful not to change anything about the animated objects - otherwise Blender will discard the cache and start afresh when you 'play' the animation, losing your bake. You should ensure that everything about your project (including the baked cache files) is backed up before you try this so as to not risk losing your previous bake if something goes wrong.