Can I use the QRCodeChimp default email content again after customizing an email?
Yes. You can switch back to the QRCodeChimp default content at any time.
Go to Dashboard > Settings > SMTP Setup > Email Content, open the relevant notification, click Customize, and select Use QRCodeChimp default.

QRCodeChimp will then use its standard subject and email body for future emails of that notification type.
Your previously saved custom content is retained. If you later select Use custom content again, your last saved custom email content will be restored.