All payments can be edited after purchase. Not all fields are editable; you can’t change the tickets purchased, total cost, or transaction data, although you can add internal notes if you need to have a record of some issue handled in the purchase. Internal notes are never used on the front-end by My Tickets, and shouldn’t ever be displayed by any custom add-ons you use.
The most common reason for editing payments may be in handling Pending payments where payment has been received; if you’re tracking specific transaction IDs such as check numbers (If you’re tracking credit card numbers, you should stop immediately – this is a major security problem!), you’ll need to edit each payment individually, but if all you really need to do is mark a bunch of pending posts as completed, you can bulk edit payments to adjust this.
If a user doesn’t receive their email notification, you can re-send it by checking the box labeled “Re-send Email Notification”.
Additionally, you can send specific purchasers a personal email from their payments page. Some venues will probably rarely need this, but for events that need to verify information with the purchaser, this can be very useful.
If you need to mass email all the purchasers of tickets for a particular event (for example, if the event had to be cancelled or delayed), you can do the from the Reports screen.