When programmatically adding conditional element to webform, I get errors
It seems as if there's really no clean way to do this.  What I realized is that it was easier to just remove all existing conditions, and then re-add them all with the additional condition included.  So I started by setting:

$node-&gt;webform['conditionals'] = array(); //remove all conditions
node_save($node); //save the node, removing all old conditions
$node-&gt;webform['conditionals'] = $new_array_of_conditions; //add entire new array of condtions
node_save($node); //save the node with new conditions


This doesn't break anything on old nodes because no data or anything else is reliant upon conditions...so removing them doesn't hurt anything or lose any crucial data.