Yes, you can change the default information in the Note to Customer field in your invoices in QuickBooks Online (QBO), JS2138.
All you need to do is enter your personalized message in the Note to Customer field each time you create an invoice for your customers.

When you email the invoice, the note to your customer will appear as shown (please check inside the red box) below:

If you need help cleaning and organizing your books for tasks such as taxes or reconciliation, our QuickBooks Live Expert Assisted can provide support from QuickBooks-certified bookkeepers who offer quick answers to questions about automation, categorization, reconciliation, and more.
If you have any other questions about customizing your invoices, let us know in the comments. We'll be happy to answer them for you.