+/*
+ * \brief Modifies the value of a given Header Entry (Dicom Element)
+ * when it exists. Create it with the given value when unexistant.
+ * A copy of the binArea is made to be kept in the Document.
+ * @param binArea (binary) value to be set
+ * @param Group Group number of the Entry
+ * @param Elem Element number of the Entry
+ * \return pointer to the modified/created Header Entry (NULL when creation
+ * failed).
+ */