Тут все не так просто. Копайте в этом направлений:
Sub SetRenderer(Optional pFL As IFeatureLayer = Nothing, Optional prefName As String = "")
'
' Манакбаев У. 28.10.02 пн 18:25:28
'
Dim pRenderer As ISimpleRenderer
Dim pGeoFeatureLayer As IGeoFeatureLayer
Dim pMarkerSym As IMarkerSymbol
Dim pColor As IRgbColor
If (pFL Is Nothing) Or (prefName = "") Then Exit Sub
Set pGeoFeatureLayer = pFL
Set pRenderer = pGeoFeatureLayer.Renderer
Set pRenderer.Symbol = GetSymbol(prefName)
End Sub