HtoA lets you edit the layer names, and that’s how to generate the variance AOVs for denoising.

• Add two AOVs with the same name (I used “custom” here), but give the second one a “_variance” layer name (“custom_variance).
• Change the Pixel Filter to variance.
• Render some EXRs (in my screenshot below, I should the part of the Arnold log that tells you that the variance AOV was rendered too)
• In the Arnold Denoiser, put the AOV names in the Light Group AOVs text box.