I see there are many others that are having the same problem as me. And alas, it doesn't seem like the problem has been solved or very understood for that matter.
I want to be able to take a document, that has multiple layers, inside of multiple groups with various layers having various blending modes applied to them and from within that document, select simply two of those layers, one with a Divide blending mode and the other layer Normal, merge those two layers, but have the visual appearance of the merged layer maintain the visual appearance of what the layers looked like before I merged them.
Everytime I attempt this, Ps takes my Divide layer, reverts it back to Normal and then merges the layers, thus changing the appearance of what it was before the merge. This is not the desired result.
I understand that when you flatten an entire series of layers, it applies all the blending modes and maintains the visual appearance. Is there a way to do this with just two layers instead of all the layers? If so, that would be great information. If not, why not?
How would that be possible? Your divide layer operates on all the layers below and then in turn its result is processed with whatever other stuff is happening. This is perfectly normal and short of PS taking the step of merging all layers below automatically as a copy and applying the blending mode, I see no way how it would be technically or mathematically feasible to retain the result of such operations. And the answer is all right there - duplicate whatever layers are involved before the divide and merge them, then use the divide layer's mask to create a selection on it and merge that further with whatever layers you have on top...
Short answer: No.
A "layer" with a specific blending mode implies a sequence of math operations on a given pixel. Think of the visible pixel R, G, and B values as the result of a potentially complex math formula that combines numbers from each layer in complex ways (those ways being defined by the blending mode you've chosen). You can't always simplify particular factors of your choosing in a given math formula.
The next step is to examine why you would want to do so. Perhaps there's a more direct way to achieve your goal that would avert the need entirely.
Another possibility, if the effect of several layers together is something you'd like to manipulate as a unit, is to Group the layers.