Load most detailed lod tiles inside bounding box

I would like to develop a function in Unity that user could set a bounding box into a scene and then export all the tiles meshes from that region (inside and overlapping) into single combined stl/fbx file? For that Unity would need to load the most detailed tiles that are inside that bounding box and then somehow generate a list of tiles which are inside or overlapping the bounding box. Is this possible with current Cesium for Unity?I think that getting mesh filters would be straight forward with Unity and for exporting the tiles I will use some other Unity plugins.

That would unfortunately be a violation of the terms of use of most tilesets.