No you can’t do the way you want, because after the channel it is not a Texture (texture object stands for the whole texture) anymore but a sampled portion of the texture at specific UV position (so not the whole texture).
It is something conceptual actually.
This is what I have told:
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that material function does the same thing:
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What you can do if you want to isolate the texture stored in that channel is to draw a material selecting the red channel (or any other) and use the material in a blueprint callind DrawMaterialToRenderTarget and use the render target right-clicking on it and choosing Save As to create a copy of the texture now stored into the render target.