On #1 you could modify the script so it uses a dialog prompt to take setup values from a user like display name. Apps Script has a built-in propertery service you can use https://developers.google.com/apps-script/guides/properties

On #2 nothing that can be added to the script to prevent this happening. My recommendation would be to follow ‘best practices’ guidance for bulk email distribution e.g. https://support.google.com/mail/answer/81126