Email subject in contact form change?

I would like to know if there’s a short code I can use to change the mail subject in all the contact form elements I’ve placed in a live website, instead of changing each element individually on 20+ pages. This is the email that’s sent to admin contact with the users information filled inform the form…

“E-Mail Subject
You can define a custom Email Subject for your form here. If left empty the subject will be: New Message (sent by contact form at Custom Home Builders)”