No. Deans of HLS and YLS are on record saying they don't want an addendum for this. You clearly studied more or didn't have a previous obstruction. Either way, admissions committees don't want addenda for this!
... instructions as it pertains to addenda and/or optional statements. If ... instructions invite any statements or addenda otherwise relevant to an applicant ... . Where the optional statement or addenda language is limiting to very ...
You pay when your application is complete, all addenda are attached, and you are ready for the app to be sent to the school (at which point, you cannot make changes to the original applications.)
Michigan doesn't necessarily see that big of a difference w/ LSAT scores once you are in the 99th range (Dean Z said that she thinks its more questionable to retake if your first score is that high). Unsure about NW.