First, I'd have to question why you'd have 100 separate mailmerge main documents if they so often need processing as a group. Why not combine as many as possible into a single document?
Second, you could use macros to automate both the linking of the copies to the user's mailmerge data source workbook and to drive the merge process. Such a macro can even save the files - the
Send Mailmerge Output to Individual Files topic in the
Mailmerge Tips and Tricks 'Sticky' thread at the top of this forum (
https://www.msofficeforums.com/mail-...ps-tricks.html) contains a macro for doing that kind of thing.
Third, you can select multiple files in File Explorer, then right-click and choose Print - without having to open the files. This won't be particularly helpful for mailmerge main documents, though, as that won't necessarily result in the relevant records being printed.