Hi Yip,
You can clean up incised carving but as Mike wrote, the sharp "V" chisel should not require it. However, I find that I have to go back to add highlights and details. For example, often I want part of a scroll to widen for accent. I can accomplish that mostly by laying the "V" chisel more on its side as I go around that part of the curve. Yet, many times that is not enough and I want a wider stroke so I go back and cut the curve wider. To do that I often use a gouge which fits the curve and stab it in at an angle. That is a way to clean up at least some of your incised carving. So you can do at least two things both require you to make sure your tools are razor sharp. You can go over your already cut lines with a properly sharpened chisel or you can stab in accents with sharp gouges.
dave