Dim DM_FACT As SwDMClassFactory = Nothing
Dim DMAPP As ISwDMApplication = Nothing
Dim DMDOC19 As ISwDMDocument19 = Nothing
Dim DM_KEY As String = "..."

DM_FACT = TryCast(Activator.CreateInstance(Type.GetTypeFromProgID("SwDocumentMgr.SwDMClassFactory")), SwDMClassFactory)
DMAPP = DM_FACT.GetApplication(DM_KEY)
Dim full_path_assy_comp As String = ".....\CURVE.SLDPRT"
DMDOC19 = CType(DMAPP.GetDocument(full_path_assy_comp, SwDmDocumentType.swDmDocumentPart, True, Nothing), ISwDMDocument19)

Dim cfMgr As ISwDMConfigurationMgr2 = DMDOC19.ConfigurationManager
Dim conf As ISwDMConfiguration16 = cfMgr.GetConfigurationByName("DEFAULT")
Dim names As String() = CType(conf.GetCustomPropertyNames(), String())
For Each prop As String In names
Dim val As String = conf.GetCustomProperty(prop, SwDmCustomInfoType.swDmCustomInfoNumber)
MsgBox(prop + "=" + val)
[It show me actual value of 90.00 for alfa ]
Next

conf.SetCustomProperty("alfa", "57.00")
DMDOC19.Save()
For Each prop As String In names
Dim val As String = conf.GetCustomProperty(prop, SwDmCustomInfoType.swDmCustomInfoNumber)
MsgBox(prop + "=" + val)
[It show the new value of 57.00 ]
Next
DMDOC19.CloseDoc()

[When i openthe part in SW .. alfa is still 90 ]