A recommendation: I think there should be a list of ranks as default, but they can be renamed, removed, and added by leaders, to work specifically for that regiment. The creator of a regiment group should get the ability to change settings in what players can receive certain classes + benefits, as well as being able to change the "creator rank" to someone else.
Or maybe a leader can start a poll on which rank they would like to either add/change/delete whatever, and other leaders may have the chance to vote on that so that it becomes the default. The leader would also probably have to provide a rationale for the change, and include sources if its historically accurate or whatever..
Not all regiment/regiment leaders want to use the same ranks, so I don't think they have to use all the same ranks. It should be formatted to work for specific regiments, otherwise, special ranks that are regiment specific, whatever they may be, wouldn't be available. I also think that sub-groups/detachments/regiments should be available. The most obvious one would be artillery, or skirmishers, or cavalry, but it also extends to things such as the Zouave Cadets for the 11thNY, which functions with separate ranks from the rest of 11thNY. So I think there should be sub-systems in the regimental ranking structures, and I understand that this works for some regiments and their artillery detachments, for example.
I think a diagram could help explain... I might work on one later, if this was confusing. I should also include that the format of a regiment should be able to change. This works for things like the Tercios (I apologize if I misspelled that). This definitely requires a diagram of sorts, I'll be sure to make one later.