Not recommended, but you can use the CDN script to add again the FA 4.7 icons on your site.
Copy the script you will find in your email and paste it in the /head tab of your theme
<script src="https://use.fontawesome.com/xxxxxxxxxx.js"></script>
You need also to whitelist the source (https://use.fontawesome.com/xxxxxxxxxx.js) adding the URL in the site setting content security policy script src to make the script work.
Then you will be able to use the old set of icons on your site.
PS: Note that there is no guarantee that this workaround will continue to work in the future.