Set SwDim = SwSelMgr.GetSelectedObject2(1)→ SwDim as Dimension → don't set center dimension.

Private Sub ll0220()
  Dim SwApp As SldWorks.SldWorks, SwModel As ModelDoc2, SwDraw As DrawingDoc
    Set SwApp = GetObject(, "SldWorks.Application")
    Set SwModel = SwApp.ActiveDoc
    Set SwDraw = SwModel
  Dim SwSelMgr As SelectionMgr, DispDim As DisplayDimension, SwDim As Dimension
    Set SwSelMgr = SwModel.SelectionManager
    Set SwDim = SwSelMgr.GetSelectedObject2(1)
    Debug.Print SwDim.FullName

   
    With SwDim
      
    End With
   
End Sub

************************************************************

Now can traverse displaydimen → DispDim.CenterText = True

Private Sub lll0220()

  Dim SwApp As SldWorks.SldWorks, SwModel As ModelDoc2, SwDraw As DrawingDoc, SwFeat As Feature

    Set SwApp = GetObject(, "SldWorks.Application")

    Set SwModel = SwApp.ActiveDoc

    Set SwDraw = SwModel

  Dim SwView As View

    Set SwView = SwDraw.GetFirstView

    'Set SwView = SwView.GetNextView

  Dim DispDim As DisplayDimension, SwDim As Dimension

    Set DispDim = SwView.GetFirstDisplayDimension

    Do While Not DispDim Is Nothing

       Set SwDim = DispDim.GetDimension

       DispDim.CenterText = True

       Set DispDim = DispDim.GetNext

    Loop

End Sub