But when you make custom fields with types you always get wpcf before the fieldname. So the Yoast field is not edited, but the field wpcf-yoast_wpseo_focuskw is.
But not with the generic field you suggested. I never discoverd the button 'Manage on-Toolset Post Fields' in the bottom of my list with forms. Now I read the instruction once more and discoverd it. I would expect this button on the general configuration tab forms and not on bottom of my list of forms.