In general, there are two types of editing: Editing for customization of the page for your book and editing to fix an error/mistake. The former requires "forking" the page and the latter requires finding the original page to edit (discussed next section). Which approach to take depends on which category your edit(s) fall into. The former is address in this page and the latter requires editing rights to the source, which can be provided as long as you are willing to curate for the library and the users that use the content.
A transcluded page can be converted to a normal editable page with a copy of the content from the mirrored page by "forking" the page. Since transcluded pages are the default for the OER Remixer, this is a useful activity for editors of the library. Let's consider the first chapter's exercise set in the OpenStax Calculus text.
If the transcluded page is tagged properly, there will a "forker" icon next to its name as shown below.
If you press that icon (and it may not exist), a window should pop up that lets you ":fork" the page (copy the source content from the source pages into the translcuded page). This effectively removes the trancluded nature of the page and make it a customizable/editable page.
If that icon is not on the title, the forker can be accessed via the the "Options" pull-down menu on the black bar. This will open up the same popup window with the same effect.
As with all edits, the effects of forking can be undone by going to the "Revision History" option under the same "Options" pull-down menu and reverting to the previous version of the page.