Each asset type in UE4 is represented by specific class, for example static mesh is UStaticMesh so in blueprint it will be “StaticMesh”, make a object varable of that class and in property editor you will have static mesh selection, ofcorse you will still require code to swap the mesh when varable change, It’s hard to do it in blueprint as there no editor events in it but, Construction Script is triggered on every change of actor in editor so use that. Thsi won’t work on runtime, for runtime you would need to make a function for setting the mesh so that function would do the job.
In-game solution would require more work as you would need to gett all static mesh assets made make menu of it