After FBX refresh the materials changes the order.

Hi there! I’ve a FBX scene (a home with an yard with a multiple materials) which I imported as a combine mesh from MODO. In UE I assigned materials by elements. In my plan in the hereafter to modify in MODO the existing mesh, to add some new objects, to rearange, to group and then to refresh FBX in UE. But my problem is when I even add a new object in the scene I get disorder the materials, and I need again and again reassign the materails. Which is the right way to refresh combined mesh in UE? How to hold materials by mesh ID? That if I need to group objects in MODO and it will force disordering the materials?

The best way to design a scene should be create asset individually. Put them in UE editor.