Custom style invoice which has a footer with figures which relate to the data in each invoice created. So I change the style invoice to suit each time?

Hello there, @communityoil.

I replicated your situation using my sample company file to confirm that changing the footer on the template will also update the copy of sent invoices in QuickBooks. 

So the existing transactions can retain its figures, I recommend creating a separate template with the new data and use it moving forward.

Here’s how:

1. From the Gear icon, select Custom Form Styles.
2. Click the New style drop-down and choose Invoice.
3. Go to the Content tab and select the footer area of the invoice.
4. On the Add footer text box, enter the new figures.
5. Hit Done to save the changes.

Once done, make the newly created template your default. Follow the steps below:

1. From the Custom form styles window, click the Edit drop-down next to the template.
2. Select Make default.

You can check out this article for more information: Add, customise, or remove logos on sales forms..

That should get you pointed in the right direction.

Please let me know how everything turns out. I'm always here to keep helping. Have a good one!