Can I change my response after sending it?
No. Once it reaches the payment processor it is forwarded to the card issuer as sent. Preview the PDF before you sign.
From the guide Payment Disputes & Chargebacks.
The decision
The card issuer decides, usually within several weeks, and Seayora emails you the outcome. Seayora’s suggestions say what the card network asks for; they are not a prediction of the result. A decision can be overturned on appeal: if a dispute decided for the cardholder is later decided for you, the payment counts as paid again everywhere — a contractor’s receipt stands again and the customer is told, and a books invoice is paid again.
What you sent is kept with the dispute: the response PDF and your files, each with a fingerprint. The files themselves are deleted 180 days after the decision; the record of what was sent stays.
Read the whole guide: Payment Disputes & Chargebacks