Does not allow for the change of bank account numbers in customer header or billpay via Intuit.

Welcome to the Community, info2059.

After you create a bill and select Schedule Payments, you can add or update the account you pay from.

Here's how:
 

1. Go to Select account to add a bank account, then choose Change account to update to a different account, Add a bank account to add a new one, or Enter bank account info manually.
2. Follow along with your presented steps and enter any necessary information.
3. Go to Payment account in QuickBooks and select an account from the chart of accounts to sync your payment info, then click Next. You can also hit + Add new to create a new account to track bill payment details. This enables auto-matching of transactions and sets up the chart of accounts correctly to keep your books accurate.
4. Select Save.

I've also included a detailed resource about working with QuickBooks Bill Pay which may come in handy moving forward: Learn about QuickBooks Bill Pay

If there's any additional questions, I'm just a post away. Have a great Thursday!