Add (change template) inlet from template to a junction without erasing the part family for the existing object

For example, in a model exported from Civil 3D, HEC-22 inlets need to be added to 100s of structures. The workflow is:
1. Create an Object Template for the HEC-22 inlet
2. Right click each structure and change template to add a HEC-22 inlet

The problem is this action erases the structure's existing part family that was mapped from Civil 3D. Structures with different part families may need the same HEC-22 inlet so it does not make sense to create templates for the same inlet for every part family. I just want to be able to apply the inlet template to various structures without it erasing the part family.