Imran,
If you select all the objects under the Art Smart Object, the Scale Tool> Attribute Manager> Object Axis> Per Object Manipulation, then you can all objects at once that need the same scale amount. Do not scale the Art Smart Object, it will produce new instances. Do this with a copy of your file first, as I have nothing from your side here, it is really difficult to say anything.
Material
https://www.youtube.com/watch?v=sua_pcai8OE&list=PLD428BE966FF3B1E9&index=100
TH Art Smart Object writes this color into the Sweep or Extrude Attribute Manager> Basic> Color. This is the same color that the Ai file has applied to the Path (spline). No idea why you have changing colors.
If you have a Material in the material Manager that you need to replace on many objects, do the following. Select that Material in the Material Manager.
Go to material Manager> Select> Select Material Tags/Objects
In the Attribute Manager, the Material Tag should be visible.
Drag the NEW material into the Attribute Manager> Tag> Material field. Done.
So, it’s midnight here, My best wishes.