CAD tip # 11211:

sureq = MessageBox.Show("Do you really want to change units in the whole assembly?", "iLogic", MessageBoxButtons.YesNo)
if sureq = vbYes then

' preset units
 oUOM1 = UnitsTypeEnum.kMillimeterLengthUnits ' or UnitsTypeEnum.kCentimeterLengthUnits
 oUOM2 = UnitsTypeEnum.kGramMassUnits ' or UnitsTypeEnum.kKilogramMassUnits
 oPrecision = 3

 dim openDoc as document
 openDoc = ThisDoc.Document
 openDoc.unitsofmeasure.LengthUnits = oUOM1 
 openDoc.unitsofmeasure.MassUnits = oUOM2
 openDoc.unitsofmeasure.LengthDisplayPrecision = oPrecision

 dim docFile as document 
 For Each docFile In openDoc.AllReferencedDocuments 
  ' parts only
   If docFile.DocumentType = kPartDocumentObject Then 
     dim FNamePos as long
     FNamePos = InStrRev(docFile.FullFileName, "\", -1)                         
     dim docFName as string  
     docFName = Right(docFile.FullFileName, Len(docFile.FullFileName) - FNamePos)       

     docFile.unitsofmeasure.LengthUnits = oUOM1
     docFile.unitsofmeasure.MassUnits = oUOM2
     docFile.unitsofmeasure.LengthDisplayPrecision = oPrecision

     docFile.Rebuild
   End If
 Next     
 iLogicVb.UpdateWhenDone = True

end if