Re: Can the course behaviour change depending on completion status?

If you set the navigation to Restricted, the user will have to go through the entire course in order. 

• With Restricted navigation, the user can click the built-in Menu to return to any previously viewed slide. But they can't click the Menu to advance.
• Also, the program will disable the NEXT button on each slide until the timeline ends. But that will only happen the first time the user visits the slide. (Note: it will work that way even if you don't show the built-in Menu. You can also use triggers to ensure the user finishes an interaction, if that's needed.) 
• After the user completes the course by viewing all the slides, they'll be able to visit whatever slide they want/need to. 
• The Navigation setting is in the Player: 

As long as your LMS lets someone relaunch a completed course, that should do what you want: ensure someone views the content the first time they go through the course, yet be able to view any content when they return.