Sry Mike, this one slipped by, its been a while, you should just be able to add this at the end:
else{add_action('wpcf7_mail_sent');}
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Artaudiomomo:
As far as I know the way not to loose modifications to a plugin functions.php file is to save your add-in code, update and then re-add the code. Some plugins are set up to work within child themes, but I don't know about CF7.
There are instructions in the code on how to set this up in CF7, basically:
Create a form and use the default CF7 name and email.
Create a radio select on your CF7 form and name it 'opt-in' with the options 'yes', 'no'.
That should do it.