It is possible to add some custom text to the invitation email that is sent to manually added participants.
First, you'll need to head to the Backstage area of your hub.
Once you're backstage, click on the Settings option in the menu and then scroll down to the Emails section and click Edit.
Enter your custom text in the Invitation message field. Line breaks and formatting are not supported — your message should be just one paragraph.
Below is an example of what the invite email looks like with a custom invitation message added (the text outlined in red).
Please note, the banner image is not currently editable.