Hey, @MixedWorlds .
Thank you for sharing this feedback and I’m happy to send this over as a feature request to our developers. I can appreciate that you prefer not to use an app and Shopify should have something like this. You can also do this by making a couple of theme adjustments and creating a template for invoices.
You can do this by using the cart page to collect more information from your customers, which will allow you to capture the VAT number. After that, you can use our free app, Order Printer, to show the cart attributes that was captured on the invoices. If you need to show VAT prices before customers add any items to their cart, you can also modify your theme to show VAT prices on your product pages. Please note that these are an advanced coding guides that is not supported by our Theme Support team. If you have limited knowledge of HTML, CSS, Javascript, and Liquid, feel free to hire a designer or developer from Shopify Experts.
If you have any more questions on this topic, feel free to reply to this thread and I’ll be happy to help.