In fact any available option, figuring out in Military Option pages, but the first seven ones cannot be activated/Selected.
It can be clearly evidenced in Coalition Military Options available in 1813 default Campaign, where 8 options figure out.
The eigth enlisted option, top-bottom enlisting order, cannot be activated: "Coalition GHQ orders an offensive" in the example.
Of course as other options are fired, allowing to scale up "Coalition GHQ orders an offensive" option to a roster position 1-7, then it can be activated, too.
While hope to see an official fix with next patch, I please to post a temporary editing modding solution I could try for my Germany 1813 Hist Mod scenery, where I have 9 available military options, while only first seven ones are selectable.
JastaV