I use the uvmap/unwrap modifier in for texture size/tiling, and adjust it before merging the model, then I apply other changes in UE4 via asset actions/property matrix if want to keep the imported ones, but change two-sided/emissive etc.
If export via DWG 2013 with solids enabled “DWG export settings in Revit”, convert all materials to “standard”, you can apply diff/spec/gloss/bump maps etc from , and since the model is cleaner it´s easy to select polys/modify if want to change something.
I have also setup a material library mixed with materials from Markedplace/example scenes etc, so there are loads of available architectural materials if merge the different ones offered in the “learn section alone”
You can also use this addon in Revit, it will join components via material, and since all are “standard” the textures will import, but you might have to adjust "smoothing , and the triangulation on some meshes.
://lumion3d/revit-to-lumion-bridge/