An RDO-defined definition overrides a macro-defined definition of the same name. For example, if you try to install a definition for a VTAM® terminal that has the same name as a non-VTAM terminal, the VTAM terminal entry overwrites the non-VTAM terminal entry.
If you INSTALL a group while CICS® is active, the resource definitions in the group override any of the same type and name already installed.
When an existing resource definition is replaced in this way, the statistics associated with the old resource definition are transferred to the new definition. If a PROGRAM definition is replaced, the program is relocated on the library and loaded when the new definition is referenced for the first time. In effect, the new definition implies a NEWCOPY operation. The same rules apply to map sets and partition sets.
It is probably unwise to have more than one resource definition of the same name on the CSD file, even for different resource types. You must keep PROGRAM, MAPSET, and PARTITIONSET names unique. If you have, for example a PROGRAM and a MAPSET with the same name, only one of them is available to CICS. As far as names are concerned, after installation these definitions are treated as if they were the same resource type.
The only reason why you might have more than one resource definition of the same name is if you have alternative definitions of the same real resource, with different attributes. These resource definitions must be in different groups.