Entering the Opportunity Role on the Lead

I have not tried this and the code below is NOT tested, but, I would use an after_relationship_add logic hook.

from Opportunities, when the Opportunity is related to a Lead:

• fetch the Lead
• find the contact_id on the Lead (this will be the Contact that the Lead was Converted to)
• find the contact role that you set in the dropdown on the Lead
• update the role:

  • $oppBean->contacts->add($contact_id, array('contact_role' => $contact_role));

So your after_relationship_add logic hook in Opportunities will look something like:

function updateContactRole ($bean,$event,$arguments){
    if($arguments['related_module'] == 'Leads'){
        $leadBean = BeanFactory::retrieveBean('Leads',  $arguments['related_id']);
        if(!empty($leadBean)){
            if(!empty($leadBean->contact_id) && !empty($leadBean->contact_role_c)){
                $contact_role = $leadBean->contact_role_c; //get the contact role from your Lead
                $contact_id = $leadBean->contact_id;  //get the contact_id
                //set the contact role on the Opportunity Contact relationship
                $bean->contacts->add($contact_id, array('contact_role' => $contact_role));
            }
        }
    }
}    

I have not tried this and the code below is NOT tested, but, I would use an after_relationship_add logic hook.

from Opportunities, when the Opportunity is related to a Lead:

• fetch the Lead
• find the contact_id on the Lead (this will be the Contact that the Lead was Converted to)
• find the contact role that you set in the dropdown on the Lead
• update the role:

  • $oppBean->contacts->add($contact_id, array('contact_role' => $contact_role));

So your after_relationship_add logic hook in Opportunities will look something like:

function updateContactRole ($bean,$event,$arguments){
    if($arguments['related_module'] == 'Leads'){
        $leadBean = BeanFactory::retrieveBean('Leads',  $arguments['related_id']);
        if(!empty($leadBean)){
            if(!empty($leadBean->contact_id) && !empty($leadBean->contact_role_c)){
                $contact_role = $leadBean->contact_role_c; //get the contact role from your Lead
                $contact_id = $leadBean->contact_id;  //get the contact_id
                //set the contact role on the Opportunity Contact relationship
                $bean->contacts->add($contact_id, array('contact_role' => $contact_role));
            }
        }
    }
}