Probe cubemaps are baked and stored as 6×1 horizontal strip images. I'm not aware of any other tools that use this format. This can make it quite difficult to use these images with other tools.

bakedTexture represents the texture that is baked via Unity's lightmapping tools. customTexture is the asset reference provided as a custom override in the Inspector. This separation allows the probe to keep the old baked texture (to swap back to) if the custom baked texture is removed.