at least CXTPPropertyGridItemSize works this way:

 

class CXTPPropertyGridItemSize::CXTPPropertyGridItemSizeWidth : public CXTPPropertyGridItemNumber
{
public:
 CXTPPropertyGridItemSizeWidth(LPCTSTR strCaption)
  : CXTPPropertyGridItemNumber(strCaption)
 {
 }

 virtual void OnValueChanged(CString strValue)
 {
  ((CXTPPropertyGridItemSize*)m_pParent)->SetWidth(strValue);
 }
 virtual BOOL GetReadOnly() const
 {
  return m_pParent->GetReadOnly();
 }
};