Trista,
Todd is correct that once you have signed-off the note, it cannot be changed. An addendum is the way to go. Sometimes for an error like you describe, the best thing to do is to create an entirely new, corrected note (with the same date of service) and use that one, creating an addendum to the incorrect note stating that it should be ignored entirely.
Some of us would like to have AC create the ability to indicate corrections (for example, drawing a line through an error, just as with paper). Please send a message to AC if you agree that would be a useful feature.
