No, remember: just before the election, Lincoln wrote out a directive that stated that, once the election was over, he would follow the course selected by the electorate; that, if McClellan won, he would NOT push the enforcement of the war because he viewed that to be against what the people had decided in the election. To my memory (and I have to admit that I am working from memory here because all of my books are at home) he passed this directive around his cabinet as well so that they were aware of the fact that, should Lincoln lose the election, the direction of the prosecution of the war would change.
As far as the Johnston/Hood change of command, Sherman was worried more about a Confederate "army-in-being" staying in the local area of Atlanta, chewing up his rail-lines and interfering with his logistics, all the while sitting there like a rabid dog waiting to pounce on him should they be able to cut him off for very long. Sherman was relieved when Hood took over because he knew that Hood was the type of general to drive straight ahead (virtually, a Confederate Grant) and would not play the delaying game that Johnston had done so well. Sherman truly worried about and respected Johnston's ability in the defense. On a number of occasions during the Confederate retreat from Chattanooga to Atlanta, Johnston came within an inch of ambushing one of Sherman's columns and chewing it up, which would have gone a long way to equalizing the disparity of the forces.
A case in point is what Hood did with his Army once he got to Tennessee and Kentucky .. the battles of Franklin and Nashville displayed his utter incapacity to command such large forces or to make any plans other than the straight charge into the teeth of well-prepared defenses, bleeding the Army of Tennessee white at Franklin and completely destroying it at Nashville.
Sherman did not begin his March to the Sea until he was sure that Hood was headed for Tennessee and Kentucky, hoping that Sherman would follow him back in that direction. Sherman's statement (again from memory) was that, if he could be sure that Hood would go to Tennessee and Kentucky, he would give him the rations and the logistics train to do so; that General Thomas could worry about him instead of Hood hanging around the local area making foraging and resupply difficult, if not impossible.
Keeping Johnston wouldn't have automatically translated into keeping Atlanta; on the other hand, putting Hood in command virtually guaranteed that that would be impossible.
This morning, as for some days past, it seems exceedingly probable that this Administration will not be reelected. Then it will be my duty to so co-operate with the President-elect, as to save the Union between the election and the inauguration; as he will have secured his election on such grounds that he cannot possibly save it afterwards.
What Lincoln meant by this was that he would have done all his power to bring the war to what he considered a successful conclusion between November and March. He considered nothing less than a united country as a successful conclusion and in this McClellan agreed with him. At the convention in Chicago, McClellan repudiated the peace plank of the Democrat Party platform. His position was, and remained through the entire election, peace and reunification with honor. McClellan wrote that as soon as the confederate states, either individually or as a whole, stated a readiness for peace based simply on reunion, "we should exhaust all re resources of statesmanship...to secure such peace, reestablish the Union, and guarantee for the future the Constitutional rights of every state," meaning protection of the institution of slavery. The expectation was that with the election of McClellan a peace movement would spring up in the south as well and press for reunification. The expectations were optimistic, to say the least. So in the end, McClellan or Lincoln, the south was beaten. It was just a matter of time.
Sherman vs. Johnston or Sherman vs. Hood. It made no difference. Sherman had pushed Johnston back from the borders of Georgia into Atlanta itself. And then what? He would have either driven Johnston out of Atlanta, too, or would have starved and shelled him into surrender. So Sherman would have taken Atlanta no matter what. And he would have cut loose and headed for the sea regardless, because he recognized it for what it was. A psychological blow to that the confederacy would never recover from. Proof positive that the south was so weak that it couldn't stop Sherman from going wherever he wanted. Also he knew that he couldn't defend a supply line that streached a thousand miles and trying to do so would just waste his army away. So Sherman had to go deeper into the south or retreat back into Tennessee. He headed south taking only half his army with him and leaving the remainder, under Thomas, to take on the Army of Tennessee. He didn't care who commanded the southern army and where it was headed, so long as they didn't get anywhere near a northern city. So Thomas dogged the confederates during their last offensive with the sole purpose of hearding them somewhere where he could beat them. And that would have been the plan regardless.
Johnston may not have committed the blunders that Hood made, but he still didn't have the forces to make a difference. The whole purpose of the Tennessee campaign was to stop Sherman and to attract recruits to rebuild the army. The first purpose was futile to begin with and the second was a dismal failure. Hood made it easier for the Union but Johnston would have failed almost as badly.