Need help editing HDR cubemap mip chains

I’m trying to find a way to edit the mip chain of an HDR cube map. Essentially I would like to make the mip chain darken the further down the chain it is.

Related Question A: Does the editor import/export an HDR image with a mip chain?
Related Question B: Is there an editor out there that will import / export / edit an HDR image with mip chain?
Related Question C: Would I need C++ help to create my own Mip Gen Settings so my edits could be done in the editor?

Cheers,

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