How to align the decal uv with the vehicle's _vmask texture?

[HatsuneKid]

I need to make some modifications to the deacl in blender. However, after converting the model from i3d to obj, it will lose the UV information of the second and third layers.
So how can I fix the decal uv to align it with the trailer uv? In order to restore them to original state, the texture positions of the dirt stains can be aligned with each other.

[DzInLa]

Have a copy of the original decal (before editing) for reference.
Don't change the default UV Map for the dirt.
Create the 2nd and 3rd UV Maps for the decals.