In DevTest / VSE , you need to use multiple request matchers and routing actions. Configure request data argument matchers (JSON/XML/header/body fields), then send the matching requests either to a specific virtual response or to a live invocation step. scripting is required.
If your use case is mainly conditional routing + partial mock/proxy behavior, Beeceptor is much simpler. We use as an alternative and faster modeling such things. You can match any request parameter (headers/body/query) and decide per-request whether to mock, proxy to upstream to generate response.