This is an old thread, but I could not find anything about a script to import classlist files into an existing course.
Note: It is currently set up to add users which do not exist, but to skip (and not replace) users which already exist in the course.
I have done some initial testing when the script is put in webwork2/bin and run using syntax like:
./importClassList.pl courseName path_to/classlist.lst
Any feedback would be welcome.
Tani