Disable a button upon restart of a course?

I am building an exam to be administered at the end of an instructor-led lesson. Students have the option to test out of the lesson by taking the exam as a pretest before the lesson begins; if they fail, they have to sit for the lesson with the instructor before taking the exam again as a final exam. My intention is to use the same question bank for both the pretest and the final. On the first slide, students will click on either a "pretest" or a "final exam" button and go to the corresponding instructions page (since the instructions are slightly different for the pretest). They click the "begin exam" button, and the questions come from the same draw and the exam goes to the same results slide regardless of whether they clicked on "pretest" or "final exam" on the first slide.  I cannot include a retry button: students are allowed only one attempt at the pretest, and while they are allowed multiple attempts at the final, there are some things that they need to do with the instructor before they can attempt the final again. Students need to close out the exam when they are finished and I need the course to go back to the beginning when they open it again. 

I feel like I can't use the "always resume" or "prompt to resume" options. This would take the user back to where they left off, which would be the "your score has been recorded; exit now" page. I would have to put a "return to the beginning" button on there, but that would enable students to attempt the exam again in that same session, which they aren't allowed to do. What I'd like to do is this: have the exam reset and the course go to the first slide when reopened, but with the "pretest" button disabled. Is this possible? If not, what can I do to both a) keep a student from attempting the pretest a second time and b) require students to have to re-open the course to take the exam a second time (whether it's as the final after failing the pretest or as a second attempt at the final)?