You can choose to Import a .beam as loadable families.
BEAM will use by default the generic models and mass templates located in: C:\ProgramData\Autodesk\RVT XXXX\Family Templates\English
Importing as loadable families will place family instances in the project with the name, category and parameters assigned with BEAM in Rhino.
These families can be edited by the user like a normal Revit family.
Using the append family geometry option will add the .beam geometry to existing families in Revit without replacing all of it. Using this feature is possible to add missing or new shapes to a family directly from the project.
By importing via BEAM a family that already exists in the project will update the the family without placing it again. This is true even if the family was moved or copied around. It will perform like Load Family.