Many of the local militia units were only company sized organizations, some clustered as state militia battalions. When and if such units offered up their services to the Confederate central Govt as quota for a given state. These frequently were combined with other such units to create a battalion or full Regiment strength unit. and designated as such by number and state of origin. The existing officers within these organizations frequently retained same, if they chose to stay. Many had joined the local militia units as a symbol of social status or affluence, and many bailed out and resigned rather than be ordered away from their local area to some distant battleground. So wasnt rare to find notible officers suddenly vanish from the rosters as the unit was being accepted into Confederate service.

Occasionally some units had to be restructured to meet the general organizational structure then in play if they originially had something different. Example there were some state militia units that had a dozen or so surgeons affiliated... or 3-4 Majors... So some tweeking was required to conform to the Govt standards.

If the militia unit was Battalion sized... sometimes taken as is... and/or utilized as a core to build up to Regiment strength by adding other orphaned individual companies to create a "new" designated Regiment.... Elections generally held to determine whom from within would be commanding and staff the new Regiment...
There wasnt a single format or designated plan since many of the local militia units differed in organizational structures, and sizes thus handled/detemined from what existed transformed into what was now required to fit into. A good range of variations frequently found...

Frederick