QUESTION:  How to copy Feature Definition from one DGNLIB to another in Explorer in OpenBridge Modeler?

ANSWER:  In OpenBridge Modeler (OBM) we have an Import/Export option for Feature Definitions in Explorer. 

To have the Import/Export option for Feature Definitions in OpenBridge Modeler > Explorer, then you will need to edit the configuration file to add _CIVIL_STANDARDS_IMPORTEXPORT = 1  (Bentley provided configurations: _Bridge Default Standards - Imperial.cfg or _Bridge Default Standards - Metric.cfg which is located in C:\ProgramData\Bentley\OpenBridge Modeler CE 10.11\Configuration\Organization-Civil\ folder).

Alternatively, this variable can be set by creating a new configuration variable within the software. Select File > Settings > Configuration > Configuration Variables > New and add _CIVIL_STANDARDS_IMPORTEXPORT at Variable and setting New Value =1 then selecting OK.