Default Unchecked the "Please notify me of upcoming specials and offers" in the Web Store Registration Page

To Default unchecked the "Please notify me of upcoming specials and offers" in the Web Store Registration Page  1. Navigate to Setup > Site Builder> Themes > Edit the active Theme > General Tab > Addition to Head, Insert the sample script:

<script type="text/javascript"> function uncheck() { document.getElementById("emailsubscribe_fs_inp").checked=false; } </script>
Note:
-This will force the field to unchecked by default
- emailsubscribe_fs_inp is the ID of the "Please notify me of upcoming specials and offers" checkbox

2. In the tag attributes field, add an Onload attribute:

onLoad="uncheck()"
3. Save