Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See Parameter IDs.
Parameter: Download Location
PREF_BROWSER_DOWNLOAD_LOCATIONParameter: Clear Downloaded
PREF_BROWSER_CLEAR_DOWNLOADEDParameter: \u27F3
PREF_BROWSER_RECALCULATE_SIZEParameter: Show Unavailable
PREF_BROWSER_SHOW_UNAVAILABLEParameter: Preview Width
PREF_BROWSER_PREVIEWWIDTHParameter: Preview Height
PREF_BROWSER_PREVIEWHEIGHTParameter: Projects as Watch Folders
PREF_BROWSER_WATCHFOLDER_AUTOMOUNT_DOCUMENTSParameter: Tree Navigation Open by Default
PREF_BROWSER_TREENAV_OPEN_DEFAULT