You won't want to tell your client this, but it *is* possible--just an awful
lot of work. To do it, you would have to unlink the TOC (Ctrl+Shift+F9),
which of course you would not be able to do until you are *sure* editing is
complete (and even then I would be careful to retain a copy of the file with
a "live" TOC field as backup) and then edit it manually. Changing just the
page numbers would not be too challenging, as that can be done with column
select (Alt+drag), but changing the leaders would be a real pain.