I think your questions are a bit hard to answer as there is no one condition and no one iundrelying pathology. It is a very complex set of problems and so ther is no one simple biomechanical adaption. If you are talking about purely postural changes due to movement impairment syndromes and where there is no underlying pathology such as Schuermanns then increased thoracic kyphosis tends to go with increased lumbar and cervical lordoses. theris likely to be length related weakness of the erector spinae at the thoracic level and protracted, downwardly rotated shoulder girdles with length related weakness of the lower and mid trapezii. The patient is likely to have limited full active forward elevation of the shoulders due to lowrer trap weaknesses and tightness of the pectoral muscles, lat dorsi etc.at the neck the neck extensors and sternocleido mastoid may be overdeveloped producing a poke chin position while the deep nck flexors are weak. At the lumbar spine there is likely to be over developed erector spinae but weakness of the lower abdominals and the hip may also have muscle changes. As you say the pelvis may be tilted anteriorly. But what causes what or is it a total motor pattern.
But you have to assess for all these things