Plant 3D use styles to managed how parts and assets are shown on the project. Most of that information is stored on the dictionaries, more specifically under NOD>Autodesk_PNP.
But the supported way to handle the styles is by the direct APIs, such as the following methods. One important note: this is valid for current/active drawings.
PnIDStyleUtils.GetStyleIdFromName
ProjectSymbolStyleUtils.CopyStyle