I'll help: Technology--specifically publishing software like Quark or Adobe InDesign and POD (print-on-demand) technology--makes it easy and relatively inexpensive to revise your book once it's published. In fact, it's so easy, you can get carried away doing revisions and become distracted from the business of authoring, which is to say, marketing. However, I do think it is wise to plan your revisions, and I've devised a mechanism for doing that.
If you are a full-service customer, I will waive my normal fees for changing up to 20 pages (regularly $1.50 per page) and for uploading files to your online printer (regularly $25.00 per upload) for a revision uploaded at least 90 days after your initial printing and again for a revision at least one year after your initial printing. (You will still need to pay any fees charged by your printer.)
Here's my thinking. If you wait 90 days after your first printing, you might want to make minor changes based on feedback from your readers and you might have gotten some juicy testimonials that you didn't have when you first printed your book Then, again, after a year, you might need to update some basic information: your contact info, website addresses, promotional material at the back of the book, or your back cover. If you don't need to make any changes, that's great. If you do, this seems like a reasonable schedule to me. And if you need to do it more often and are willing to pay the regular prices, that's okay too. The Publishing Pro.