Is it possible to save mesh related compute result in material?

qwq hi there, got a world space normal map for a skeletal mesh.
a map can’t change while the actual vertex normal is changing cuz the mesh is not static.
causing the diffusive light intensity on the mesh surface to be incorrect.
thought of to save the “VertexNormalWS” of original pose, and find the vector to the vertex normal of changed pose, add the vector to my map.
seems like viable but I can’t get a fixed “VertexNormalWS” of original pose, also try bake to material by it only bake simple math computes.
any help or correction is appriciated, I heard that substance designer can bake the map into tangent space, shall I try it?
——————————1 day later————————————
I tried to use blender to bake a object space normal map of this mesh at original pose and managed to make it work.
But it requires the model to have no seam, or the result is worse than ue4 , on the other hand I’ll have to bake for every mesh…
So I realize I need a method to save it as a variable or something similar qwq