2 same scenes with different skybox

Hello everyone,
I am creating a racing game and I have 2 same scenes (I copied first scene) with different skyboxes. and I don’t want to generate lightmaps 2 times because it will increase game size and I am afraid it my overwrite my first scene lightmaps, as currently second scene using first scene lightmaps. In second scene I just want to use same lightmap of first scene with just different skybox. please help me how to achieve this.

hello anyone?