How do I change the heading of a front or back matter section, for example "Acknowledgments" to "Special Thanks"?

From version 1.9.24, open the book's page, hover the section's row in the chapter list and click its pencil icon (for example "Edit the Acknowledgments"). At the top of the editor, click the section's heading, type the new one, such as "Special Thanks", and press Enter. The new heading is used in the contents page, in every export and in your translated editions. To go back to the usual heading, press "Reset to default heading" next to it; it prints in the book's language again. In an older version the standard headings could not be renamed.