To clarify - the nz.co.fuzion.extendedreport extension offers Editable Reports for Activities and Events - but not for Participants.
Eg with the Events report you get fields like this
Another option would be to try Drupal Views and Views Bulk Operations. I am pretty sure we have made it work for an 'event register' ie have a list of folk who are Invitees, ...
The answer posted by Kainuk sounds like a bug in civicrm. After it is fixed and still the "clear" option is not visible, make sure the custom field is not set to "Required".
Required custom fields do not have the clear option displaying on the radio custom field.
The difference is in the definition. The color field has the Options Per Line set. This has as a side-effect that it disables the clear box (and the change options wrench). Clearing this field makes the clear option return.
The Contact Form 7 integration basically takes all fields from the form and sends the data to CiviCRM. So basically you have 2 options when creating forms:
Use one of the standard CiviCRM API calls, and make sure the fields on your form are named as required by the API call
Develop an extension with your own API calls and use those (with the field names) on ...