newChildDescriptors.add
			(createChildParameter
				(DevPackage.Literals.CODE_TYPE__MIXED,
				 FeatureMapUtil.createEntry
					(XMLTypePackage.Literals.XML_TYPE_DOCUMENT_ROOT__CDATA,
					 "")));

CodeType code = mymodel.getCode();
FeatureMap map = code.getMixed();
if(map.size() > 0){
    // Display CDATA
    System.out.println(map.getValue(0));
}

String newCDATAValue = '......';
CodeType code = DevFactory.eINSTANCE.createCodeType();
FeatureMap m = code.getMixed();
m.add(FeatureMapUtil.createCDATAEntry(newCDATAValue));

Command setCodeType = SetCommand.create(getEditingDomain(), mymodel, DevPackage.Literals.MODELTYPE__CODE, c);
getEditingDomain().getCommandStack().execute(setCodeType);