You can change anything on the LR afterwards, and it will show up with the new info on the data (attendance, effort, etc.). The only thing that doesn't change is the "refund" button, so if you realize you have to refund a point after the LR has been written, someone in admin has to refund the point manually.
If you have a double lesson with a student and mark them as "over 15 minutes late", we are not sure if this gets counted as the student not attending one lesson or both lessons, so it is better to:
1. write up 2 LRs with one of them marked as "More than 15 min missed" and the other marked accordingly; or
2. write a double LR and mark it as "5 - 15 min missed" so the student doesn't get penalized.