This may be useful for your case: https://docs.unrealengine.com/latest/INT/Engine/UI/LevelEditor/InEditorTesting/KeepSimulationChanges/index.html
Create a destructible cube or whichever mesh you like in content browser > Put it in the level > Add Impulse(small enough to just break the cube) in level BP to explode the mesh > Keep Simulation Changes. I havent tried this myself but this should work i think.