Hi Christine-
Are you connected to your CRM live? Reason I ask is that radical score changes are going to affect the entire database as MKTO's algorithm is partly derived from what Lead1's score is relative to the rest of the database.
If you have connected to your CRM, I would suggest making that change on a Friday so that it can re-calculate on the weekend.
As for if you should wipe entirely or try to correct, that is going to be mainly dependent on how broad your scoring spectrum is (do you have leads with a score of +5 to +100000000000) and how large a data set you are trying to course-correct.
I would suggest that you split out demographic information (like account name, title, industry etc) away from behavior score changes (how many times you do something). If you need help, there are a lot of articles and presentations on this - but at days end, you will be able to right-size your ship with a little bit of investigation work with some small batch changes to see how things get affected.
Hope this helps!