Guys, could you please evaluate my idea - is it possible or no, and if it is - I would highly appreciated if you will give me and idea how to implement it.

I have a scene built in Solaris (Houdini 20.5, Karma CPU) from different USD assets. I would like to have a 'clay' render as an AOV, additionally to a standard beauty pass. Is it possible?

I can imagine that for achieving it I need a one material which will override all the diffuse maps and replace them with solid grey color. This 'override' material need a Karma AOV Node.
But I cant imagine how to integrate that material override into a scene tree so it will not affect beauty pass.

Any help would be much appreciated!!!

I don't think you can do that
AOVs are usually either completely arbitrary unlit values or LPEs filtering the light paths of the beauty render

so if you want a pass with completely different lit material from beauty, I'd override a material in a separate render branch

Tomas, thank you very much for your answer - this topic were torturing me for couple past days, its a relief to hear it from you that it is not possible! And in general, you are the MAN, I have 7 posts/question on this board - you replied/helped at least half of them!