Although you can't import Gerbers directly, you could convert to an image format (e.g. PNG) although CS can only import bitmaps and not vector formats, so the rendering won't be perfect. Furthermore, gerber just gives you an image of the tracks and doesn't provide any information about the schematic and netlist; unless the changes are trivial it will be a struggle. Alternatively, Gerber files are human-readable (kind of) and so if the changes are minor then the simplest solution might be to edit the Gerbers with a text editor and then check them with a Gerber viewer (e.g. Gerbv). If the changes are more complex then it's likely to be quicker to start from scratch with a schematic.
