In most cases the web service that is behind the HxGN EAM screen will behave in the same fashion as the front end. For example, a web service user passes in parent Part and Condition and the backend will flip the parent part to the child associated to the Condition. However, there are exceptions to this rule.
The important thing to remember with web services is that passing in just the child part number will always work (i.e., parent Part & Condition NOT passed in). If a child Part is passed in with a Condition (which is unnecessary) the system will ignore the Condition.