Allow users to execute a particular action in a sub-workflow

In a sub-workflow, users must be able to execute a particular action by passing parameters through the job.properties.
One possible solution that I thought might work was the modify the xsd for START

<xs:complexType name="START">
<!-- <xs:attribute name="to" type="workflow:IDENTIFIER" use="required"/> -->
<xs:attribute name="to" type="xs:string" use="required"/>
</xs:complexType>

Not sure if this will work. Just a suggestion.