Okay, let me clarify the question (And thanks to the answers so far!)
Yes, they would be scanned, but when I said Modified, I really only meant adding a few pages at the start (Such as a new introduction) and adding a few pages at the end (Contact information, and what else is available)
Surely, this can be done cheaply and effectively…
(Perhaps I could MERGE my Intro into the book, and then Merge the later pages in a separate operation?)
Adobe Acrobat has a function wherein you can insert pages before, within, or after the pages you have open in the window at the time. Maybe the fourth area from the left on the taskbar, down to “Insert Pages”.
You can also convert the PDF to PostScript (e.g. with pdf2ps) and use a PostScript editor. Since PostScript files are ASCII you can even edit them by hand if you feel like it.