How can I copy an Empty with all its children, and have the hierarchy intact?

I did not find a way to set a new parent in JS nor to duplicate a parent with all its children while keeping the parent-child relationship.

I want to modify a complex object made of several meshes which i can not merge/combine into one and move it around, and i feel like the only option is to data.load the same object several times (which sound redundant and is performance-heavy).