Is there a RemoveAttributeFromMask

Hi
The following code ist working well in EB 6.7.1 to add an attribute to a type definition

EBase.ObjectItem oStartItem = myApplication.Selection[0];
if (oStartItem.Kind == EBase.ObjectKind.DeviceType)
{
oStartItem.Attributes.Add(EBase.AttributeId.TypicalCopyMergeIndex);
oStartItem.Attributes.AddAttributeToMask(EBase.AttributeId.TypicalCopyMergeIndex, "TEST";
}

My question is now: How do I revert the action? Can't see a 'RemoveAttributeFromMask()' Methode.
The Remove() Methode has no influence on the type definition dialog.