clarify config overrides

Author: razvan

modules/ROOT/pages/release-notes.adoc

@@ -427,16 +427,20 @@ Please note that Java-based products that use the JMX exporter for Prometheus ar
 
 Apache Nifi
 
-To upgrade from 1.27 to the 2.x series, the following config overrides are necessary:
+To upgrade from 1.27 to the 2.x series, the following config overrides are necessary in the new cluster's manifest:
 
 ----
 spec:
+  image:
+    productVersion: 2.0.0-M4
   nodes:
     configOverrides:
       nifi.properties:
         nifi.flow.configuration.file: /stackable/data/database/flow.json.gz
 ----
 
+IMPORTANT: Do not override this property for the 1.27 cluster version.
+
 This is necessary because the 2.x versions do not support the XML format for flow definitions anymore.
 Support for the JSON format has been addded in version 1.16 and both formats have been maintained up to (excluding) version 2.0.
 The next SDP release 24.11 will automatically take care of this step for you.