What can and can't be edited and by whom once a record is posted

Once a record is posted, it should not be edited by anyone without being exported again for corrections.

If you try and edit a payment that has been posted, you will get an error message.

Once all Payments are posted, you will get an error message on the Opportunity itself as well.

Allocations are locked down as well

Controlling who can edit a posted record

On the Fund Settings page, you can select users who will have the ability to edit a posted payment/opportunity without having to unpost them first. Select these users carefully so you don't end up getting your accounting system out of sync with Salesforce.

Controlling who can edit a posted record