After one or two hours of trial and error, here is how i succeeded to do it at runtime (instead of in construction script).
Configuration:
- a static mesh component with a child Niagara Particle System;
- in niagara system, a variable source of type StaticMesh with Source Mode to Attach Parent;
- the mesh provided must have the flag Allow CPU Access to true.
I’m not certain it is required to recreate the particle system each time you set the mesh, but i’m certain you have to call Reinitialize System each time you change the mesh.
a copy/paste version is available here: Modifying static mesh in niagara system posted by frankiezafe | blueprintUE | PasteBin For Unreal Engine
Good luck 