How to add custom query parameters to standard delivered queries?

I was told that to expose a custom field as a query parameter to a standard delivered query, I need to create a Process Extension Scenario. Is this correct?

I created an Extended BO for Service Request and added a new custom field called CustomID.

I then exposed this field to the Service Request Agent Workspace/Thing Inspector and am now able to maintain data for this new custom field.

I now want to add this field as a query parameter to the standard delivered QueryByElements service request query that is available for the Service Request Overview, so that I can create a custom OWL that renders all Service Requests that have a specific CustomID field set.

So when I created the Process Extension Scenario, I was shown the SOAP APIs that are available for the Service Request but not the QueryByElements query.

So is this the correct process to add a custom field to a query?

Thanks

Rei