Basically sky sphere is just a giant static mesh with a sky material. So remember, it was the MATERIAL that matters, so if you wanted to change the sky sphere, just change all the ■■■■ that happened in that material, are you already try to look at sky_sphere material and sky_sphere material instance also the color curve. It’s all easy to find (all placed in one folder, in Engine folder.
Ps: as what i have known that all the ■■■■ in the sky sphere is done in blueprint. No cpp at all.