Some clients pay by manual bank transfer rather than direct debit. You can move a client to manual payments yourself, without sending them an agreement email, so nothing goes out to the client while you change the setup.
How to set up a client for manual payments
Go to the Billing page and enable the client(s) you want to set up.
Choose the "Do not send" option so no email goes to the client.
The invoice status changes to "Created" rather than "Sent".
Go to the Agreements page, click the [...] menu next to that client, and choose "Switch to manual payments".
The client is now on manual payments and was never emailed. On the next billing date, the client will be sent an invoice via Xero, which they can pay by bank transfer.