So the script would be run as you start work on each project?
Yeah, as lazlow suggested, you could do this with three different users and "su" between them.
Or, you could just "chmod -w", "chmod +w" as desired in your script. It could take the argument of the RW set and act appropriately.
if [ $1 = "Chunk1" ]
chmod -R +w Chunk1/*
chmod R -w Chunk2/*
and so on.