Once an employer invoice has been issued, it's set in stone and no further changes will be made to it automatically. i.e., you can still manually add charges or credits to an issued employer invoice, but any changes to enrollments or terminations wouldn't affect the invoice.
However, if enrollment or termination changes were made after an employer's invoice was already issued for the month, and you need those changes to be reflected on the invoice, you can always return an issued invoice to draft if there is no payment history on it.
Return an employer's issued invoice to draft mode by following these steps:
Open the invoice.
Scroll to the bottom of the invoice.
Click 'Revise Invoice' -> 'Return to Draft'.
Please note: An issued invoice can only be returned to draft if there is no payment history on it.