No, do not draw undue attention to this with an addendum. It's one class and it's really not a big deal in the grand scheme of things. You want to write as few addenda as possible.
... super crucial in an addendum:
writing an addendum should show two ... , and don't write an addendum because quite frankly, you don ... to it. Especially if your addendum will only show that maybe ...
No addendum necessary, they will see your transcripts, and even if they couldn't see this in the end all they really care about is that you were awarded a degree.
I don't understand why you need to explain the first... It sounds so ridiculously minor that I've never seen an app that would require it. I'd send the LSAT addendum but I wouldn't send the other.
Oh, and don't mention that the professor who wrote you to the dean was a first year professor in your addendum though! While that provides context to us, I don't think admissions would like it. Just and FYI.
... require you to submit an addendum explaining what happened and how ... score, write an honest/ forthcoming addendum and watch the acceptances roll ...
It will hurt but you have to move on. You have to show them that it is PAST. Try to end your addendum with a positive note such as "After xxx, I finished school with a 4.0/4.0 GPA" or "I finished my last two semesters in college with straight A's."
Another way to go is just never cancel and then write an addendum and all will be forgiven. I'm way too curious a person to ever cancel or take an undisclosed test.