How do I programmatically update an existing submitted webform submission in Drupal?
Here's how to do that:

// Load the webform submissions file. The webform_get_submission() and
// webform_submission_update() functions are located here.
module_load_include('inc', 'webform', 'includes/webform.submissions');

// Load the node and submission.
$node = node_load(YOUR_NODE_ID);
$submission = webform_get_submission($node-&gt;nid, YOUR_SUBMISSION_ID);

// Change submission data.
//
// To see what's available, install Devel and run dpm($submission);
$submission-&gt;data[YOUR_FORM_ELEMENT_ID][0] = 'Update';

// Finally, update the submission.
webform_submission_update($node, $submission);


Documentation:


webform_get_submission()
webform_submission_update()