Im not an expert in the whole admissions process but I'd say don't bother with the addendum. If you really did mature and change, you could perhaps incorporate that into your personal statement, but don't dwell upon your gpa in there. You don't want to draw attention to the weakest part of your application unless you have a legitimate reason for it.

Besides, 3.64 isn't a bad gpa. It's below average for many schools, yes, but I would think it could easily be compensated for with a strong lsat score.