Should Obama do it, it will create a very interesting precedent that say a Walker or Cruz administration could use for all sorts of things.
Also, I’m not sure Lincoln counts as a conservative — after all, he really started the move from the Founders’ federal system to what we have now, essentially a unitary state with the “states” being somewhat autonomous provinces.
You can argue about the appropriate answer to that question, but not that it's an entirely relevant one.
Wars always result in an expansion of central power. That's because nations that don't expand their central power in time of war tend to lose the wars and often disappear. Reference Poland, in the process of disappearing at the same time our country was being Founded.
The question is whether Lincoln had intentions of keeping federal power permanently expanded or planned to return to something like prewar conditions asap.
I have never seen any convincing evidence that Lincoln viewed significant expansion of federal power as in and of itself a good thing, or that he intended its expansion during the War to be permanent.
Indeed, most of it wasn't permanent, with the federal government returning to something close to its original role for most of the rest of the century. It's really only with the Progressives from the 1890s on that the remorseless expansion of federal power began.
I have also never seen anything even remotely resembling evidence that the Progressives based their proposals on Lincoln's wartime precedent, or that they would not have felt as they did without that precedent. Most who have studied the Progressives find their beliefs based more on European values than anything in previous American history.
As far as your basic comment of Lincoln not being a conservative, if he were around today he'd be considered far to the right of Ted Cruz.
Where he fit in terms of his own day is a little more difficult to figure. "Conservative" in the American sense, means, IMO, conserving the ideals of the American Revolution and Constitution. The whole conflict between North and South, and the war that resulted, was basically over what those ideals were and how they should be applied to the times. IOW, what was America to be? What did "conservative" mean in 1860?