There is no way to perform a one to many mapping in the receive port. The pipeline uses the message type of the incoming message and will execute the first map whose source schema matches the incoming message type.
This allows a many to one mapping and is the basis of the normalisation pattern i.e. map into an internal schema that has a processed in an orchestration the result of which can be mapped into many different output schemas if required. The output mapping can be accomplished using multiple send ports and some form of content based routing, or using a role link.
If you wish to map a single source schema into many output schemas you will need to do this inside an orchestration or use the ESB Toolkit with a map resolver based on some message data.
How do you decide which map to run.