The article Administrative reforms and national intergration: The case of the northeast by Paitoon Mikusol (ไพฑูรย์ มีกุศล) (in: Regions and national integration in Thailand, 1892-1992) gives an interesting view on the two different styles of administration in the mueang before around 1900 and the changes during the thesaphiban reforms.
In northeastern Siam, the mueang had two different systems of their internal administration, one in use for the Lao mueang and another one for those under more Siamese control. The Lao system was introduced by the first chao mueang (governor) of mueang Tung, the precursor of present-day Suwannaphum district in southern Roi Et province. Several mueang were grouped into one principality named hua mueang (หัวเมือง, lit. head town), either for group of mueang of a specific ethnic group, or for one major mueang with its subordinate mueang.
The internal administration of each mueang was headed by the chao mueang (เจ้าเมือง), which can be translated as governor or lord. This post, though it was to be appointed by the King in Bangkok, was in fact an hereditary post of the local nobility. Usually the chao mueang had the rank of a Phra (พระ) or Phraya (พระยา). The second post was the uparat (อุปราช), normally the son or younger brother of the chao mueang, and the heir when the chao mueang died. Two further posts are the ratchawong (ราชวงศ์) and ratchabut (ราชบุตร), with the whole group of four posts named aya si (อาญาสี่). All three lower posts were appointed from the court in Bangkok, and were not under control of the chao mueang. Also the capital punishment was not in the authority of the chao mueang, but in many other fields he was quite independent in his administrative decisions.
This system ceased to exist with the thesaphiban reforms during which the local nobility was replaced by paid officials sent from the capital. At least this was the case in those parts which stayed under Siamese rule, what happened in the areas east of the Mekong which were included into French Indochina I have no idea.
The Siamese style of mueang administration will be the topic of a later post.