How to use mesh normal with VAT?

I want to use custom weight normal with VAT.

When I Export VAT in houdini, I think mesh normal (Vertex normal?) is ignored.

Is there any way to use mesh normal?

Or It’s fine if only possible to apply normal after animation is finished.

VATs exported from Houdini will export normals. Just make sure you actually add a normal attribute N in houdini.
The VAT material nodes from SideFX should have a normal output (WorldSpace, not TangentSpace).
That is then basically your new VertexNormal. As every vertex changes through WorldPositionOffset, the normal also changes each frame. So you will need to use the altered normal. E.g. if you wanted a FresnelEffect, do it with the normal from the VAT node.