No, a Universal Forwarder acting as an intermediate forwarder will not be able to route data to another index. It will just pass it along as it received it from the original forwarders.
You will need to configure this either on the original forwarders (which should be fairly straightforward if you manage those with a deployment server), or use a Heavy Forwarder as intermediate, which you then configure with props and transforms to override the index metadata field. Note: the HF solution only works if the original forwarders are UF. For any original forwarder being a HF the config would need to be on that original HF. In general: such configuration needs to be on the first Splunk Enterprise instance that touches the data, so either the first HF, or if no HFs in the path (only UF), then on the Indexer(s).
