When user try to edit details of voided transactions and click save, warning massage appears: "This transaction is voided and will remain voided even if you make modifications to it. Are you sure you want to modify it?"
SolutionThis is a standard behavior when a user attempts to unvoid a voided transaction. This is documented by in article Voiding, Deleting, or Closing Transactions, specifically: After you void a transaction, you cannot make changes that have general ledger impact to the original transaction, including changing the posting period.
To have the ability to unvoid an already voided transaction (Example: Journal Entry, Invoice, Payment, etc.) you can vote for Enhancement 29114.