Changing the variable symbol on a document will be reflected in the matching symbol in the subsequently generated balance. The matching symbol itself cannot be edited directly — it is calculated when the balance is compiled, based on the variable symbols of the document and its payment.
Procedure for a matched document
For a document that is already matched to a payment, simply overwriting the variable symbol is not enough. The link to the payment must first be removed:
remove the deduction of the advance tax document from the tax document,
unmatch the document from the payment in the bank or cash register,
make the change to the variable symbol,
re-match the document to the payment,
for the advance tax document, perform the deduction again.
When dealing with a large number of documents, the second step can be simplified using the free add-on Bulk Unmatching of Bank and Cash Register.
What to watch out for
If a single payment covers multiple documents with different variable symbols, all paid documents will inherit one shared matching symbol based on the payment. Changing the variable symbol on one of the documents may therefore not have the expected effect until you also change the way they are matched.
⚠️ Do not overwrite the variable symbol on a bank transaction just to improve the appearance of the balance. A bank transaction is a record of an actual payment, and changing it will cause a discrepancy with the bank statement.
A detailed explanation including solutions can be found in the article Matching Symbol in the Balance.