A change like that shouldn't be a big deal. A meeting to decide whether or not it constitutes a Design Change (it doesn't!) and if the new insert needs to be Validated again (likely not) and you're pretty much done from a Compliance standpoint and on to Vendor Qualification.

My guess is that the problem is more likely to be finding a vendor that can print/cut to your specification at the scale you need and, critically, who can produce it on your schedule. Any capable printer is likely already booked solid for months.

If it was a real problem I dare say they could ship with loose leaf pages detailing everything nobody reads.

Assuming they fit into the existing manufacturing process, sure. But that still doesn't solve the problem of finding a printer to print those millions of pages.