Is the registrar actually logging in to WeBWorK to add each new student? If so, at the same time they add a student they can select assignments to assign to them.
> Form the GUI i cannot do multiple assignments at one time.
Normally you can assign M assignments to N studnets where M and N are whatever, all with one go. You can do this by clicking Instructor Tools, selecting all N students, selecting all M sets, and clicking to make it so.
The other thing that occurs to me is if you were doing this through an LMS with an LTI connection to WeBWorK. The registrar would add the student to an LMS course. There would be a link there to WeBWorK. A student would follow that link, and the first time they do that it automatically creates their WW account as well as assigns all "visible" problem sets to them.