Yes, you can edit content that has been shared by others, your edits will be saved and are visible to anyone who takes the lesson after you. So please exercise caution. If possible, try contacting the user who shared this material to discuss your edits, I at least would appreciate that. This feature is probably best used for editing time stamps which should bee harmless in general. Some courses have been “locked” to prevent editing (and vandalism), for example the mini stories.