Hey, @markacrowder !
Ash here from the Shopify team.
I’m glad to help out with this question! While generally the checkout is not something we can edit on shops, we’re able to adjust the wording on themes using the language editor. This includes adding notices to certain areas, such as the shipping step of the checkout! Here’s a document in our Help Center which goes over how to access and use the language editor.
Once inside the language editor for your theme, the shipping notice can be added in the “Checkout & system” tab furthest to the right. However, you can also simply search in the “Search translations” for the area you want to edit. For this specific case, search for “Shipping method notice”. Here’s a screenshot to show what this will look like when you track the section down:
Once you add in your notice and save the page, you should then see it live on the shipping step of your checkout. I hope this helps achieve what you’re looking for, and feel free to reply back here if you need any further assistance adding in your shipping method notice.