There is no specific discussion topic for this forum, but this forum is set up for those of you who have questions or wish to experiment with modifying an open textbook.
It seems PressBooks charges a fee if you want to export your creations without a watermark:
"PressBooks is free to use, with PressBooks watermarks in EPUB, MOBI and PDF exports"
Could textbooks be created on the BC Open Textbook project PressBooks installation, or this installation is only meant to host a final creation?
Additions, deletions, reorders, and remixing are all ways to modify an open textbook, but none of those really includes revising the existing material. That can be complex, such as rewriting an entire chapter so as to take on an entirely different perspective (as economists might do), or simple, as in "gardening" tasks such as correcting spelling, grammar, punctuation, and so forth.
I see the additions and deletions as covering aspects of revising, but you are correct about the scope and difficulty. Often, revising is the most difficult challenge when it comes to modifying an existing textbook. Being more of a technician, I tend to focus on the technical challenges, like revising content in a PDF document (virtually impossible without exploding the revision scope to include reformatting the entire book), or trying to figure out how to author in LaTeX when you may have never worked with it before.