Lisa, we certainly value your idea and thank you for submitting it to us.
I have a recommendation for you. Since you are trying to maintain consistency with messaging in your invoices, you could create a Term or a Charge Type.The Term is required on every invoice and the Charge Type shows in the Line Items section of the invoice. $0 can be put in the Amount box and your message would then be added. Both options are not automatic when the invoice is created, but they do take away having to type it in the Comments box every time. It also puts the information in the Terms box or line items, which is arguably the important place on the form.
Thank you submitting your idea to us and I hope the solution I have outlined will be of some use to you. Please let us know if you have any questions or need more information and we will be happy to help any way that we can. You can reach our Legendary Client Service Center at (877)883-8337 or by email at email@example.com. Happy New Year!