I was thinking about the even that removes Patterson in 1861, and was thinking of a way to add some variation to it. Historically, since Patterson failed at his two objectives, keeping Johnston from merging with Beauregard, and capturing Harper's Ferry, how about having his removal reflecting this?
If the USA do not hold Harper's Ferry on, or by, a given turn, then Patterson is 'fired' and replaced with Banks. If the US holds Harper's Ferry, then Patterson's mission was accomplished, thereby will not be fired.
A 3-star general in 1861 will be highly prized, regardless of his ability, given a reduction of 2-star generals (for corps command).