P: Generate mask from Blend If

You can mask the luminance of a blend-if layer, but it’s much harder to mask a specific color channel blend-if. The easiest way to create a mask from a layer with blend-if applied is to place the said layer(s) in a folder group and then flatten that groups contents. It should create a new raster layer with all the opaque alpha aspects of the child ‘blend-if’ layers. From this you can just select the contents of the flattened group et viola, you have a selection of the blend-if
It’s complex, but if you have a subject on a blank background blend-if masking is most reliable and nuanced way to mask a subject in Photoshop.

I hope you can imagine what I wish to convey. 

Not exactly, I guess. 
But I suspect that you might just be trying to communicate a need for Smart Layer Masks: 
Photoshop: "Smart Masks" - Masks that are Smart Objects
Photoshop: Smart filters and live adjustments for mask layers
Photoshop: How to use a smart object as a layer mask?

I should be able to use the gradient tool and assign an adjustment layer to it as well. 

Smart Objects with Blend if -settings in Groups as the basis of a Clipping Mask can already utilise additional Adjustments (like Gradient Map) and Layer Masks. 

It stood out where I wanted the layer mask, like a bolt of lightning!
Where I want the layer mask, I mean the Blend If 'Separation Mask', is where the slider, light or dark, on either side, separates by holding down the option key, it's in that area of separation that I want the mask to take place, and I should be able to use the gradient tool and assign an adjustment layer to it as well. This is like having a calculated mobile option key selected 'live' action variable mask for compositing purposes and special effects. It's like a film or video effect action on a static image.
Ideally mini mobile masks on all sides of the sliders would be preferable, but for now just the slider option key separation gap, from its starting point, would be great! I can already see a use for it, in the example above in the top right hand corner of the image. Veronika's hair could be placed back in full, and still hold the Blend If look. I hope this explains what I've been trying to put across, even considering the other suggested approaches.
It would work as a timesaver, and change the approach given photos.

This requires a further explanation. 0-255 (this layer) / 0-255 (underlying layer)
This layer slider 255 moved to 186 as an example, a mini mask for that space is created, but consider it on hold at the moment for this discussion. The slider option key is held down on the triangle, to separate the slider for a more revealing display, to let's say 89, leaving a space from 186 to 89, where another mini mask is developed for that space, the same occurs for the 0 dark slider on the other side.
This is all conducted on the fly, with the main Blend If creation made, suspended in a holding pattern, called a 'Smart Action' (new term), (similar to a Smart Layer, in the sense that adjustment layers and filters work within a Smart Layer). The difference being that the new Blend If 'Smart Action', would have working automatic 'Space Masks' within. Mini 'Space Masks that can be filtered and adjusted, or used by tools like the Gradient tool if desired.

I hope you can imagine what I wish to convey. The Blend If initially created is like a temporarily suspended screen shot held for further effect by the Smart Action mini-mobile Space Masks. That's the best explanation I can come up with at this moment to impart what I mean. Maybe there are many other work arounds right now, but this could become exceedingly fast once comprehended. Have a good day or night wherever you live.

Here's an example of an attempted expression utilizing blend if, and how it can possibly be simplified more than what I'm trying to achieve, in an easier, smoother way.