May it be a risk to use the origin as the change address?
A transaction doesn't just identify a sending address as the source of its funds; it identifies a specific output of a specific previous transaction (by transaction ID and output number), called a txout for short.  Once a txout has been used as an input for a new transaction, nodes mark that txout as "spent" and any future transactions that attempt to spend it will be considered invalid.  (This means that the funds in the txout have to be completely consumed by the transaction; if that is a larger amount than you wanted to spend, you need a change output.  This is the whole reason to have change.)

In particular, this rule will prevent a transaction from being included verbatim in the blockchain a second time.  So any attempt to replay an existing transaction would not result in extra funds being sent.