Do my choices apply to all my classes?

No. Each class has its own. Set it in each section you teach.

You, any co-teacher on the class, and our admins.

Choose which chapters your class works on

Every class uses QuickBooks Online Step-by-Step and starts with every chapter included. To leave some out, open the class and choose Assignments.

Open Assignments
It's the button next to Class settings on the class page.
Untick Included for any chapter you want to leave out
The chapter greys out and shows Left out. The checkbox in the column heading ticks or clears them all.
Choose Save assignments
Nothing changes for your students until you save.

It disappears from the reader's chapter list, search and file list for this class.
It isn't a lock. A student can still reach its pages by page number, so don't rely on it to keep a chapter unseen.
It never opens a chapter a student's plan doesn't include. Standard-only chapters carry a Standard edition badge.
It doesn't delete anything. Bring the chapter back and the student's earlier work is still there.
It doesn't change how completion is counted. See What every number on your class page means.

Lite / Standard at the top of the class dashboard (also Class teaches in Class settings): Lite hides every chapter after chapter 10. The cog beside it opens this page.
QBO certification prep, on this page, turns the certification practice exams on or off for the class.
Chapter quizzes in Class settings: set it to Unavailable if you run your own quizzes elsewhere.

Quick answers

Do my choices apply to all my classes?: No. Each class has its own. Set it in each section you teach.
Who can change it?: You, any co-teacher on the class, and our admins.