I have to disagree. It is often necessary to reorganize the army on the fly. Commanders get killed and wounded and have to be replaced and your opponent isn't going to take a time-out to allow you time to replace them and to reorganize.
It happened on both sides, and often during the same campaign.
Here's a look at the key men who were new to their jobs in the Army of the Potomac at the Battle of Gettysburg:
https://studycivilwar.wordpress.com...omac-at-the-start-of-the-gettysburg-campaign/
Gettysburg would lead to Meade reorganizing the Army of the Potomac. He was fortunate in that he had the luxury of doing this during a lull. Lee didn't have that luxury and was forced to do so by circumstances. After all, he couldn't send a message to Lincoln to say, "Time out. Don't send any troops south until I let you know my reorganization is complete and I've had a chance to test it." He reorganized the army to make it easier for his corps commanders to control their corps. This was a function of what's called span of control. Jackson wasn't there anymore, and he wasn't ever going to be there again, so Lee was stuck with replacing him with someone. This was smack dab in the middle of the campaign "season," meaning if he didn't take the initiative the Federals would.