You can edit the default emails by going into Message Templates found in Settings -> Devices & Users -> General -> Message Templates.
Once you edit and save, you will then have to change what template you are using in your passcode compliance profile.
Like Samuel said it's possible to modify the email notifications under All Settings > Devices & Users > General > Message Templates.
Just create a new Compliance Violation User Notification. In the email body you're allowed to use lookup values.
To confirm to the company brand you can also use HTML by clicking the "show source" icon.
I have attached an HTML file that looks like this to the user, if you've got any questions, hit me up!