Add warning about using kubectl replace

docs/tutorials/object-management-kubectl/imperative-object-management-configuration.md

@@ -34,6 +34,14 @@ for details.
 
 ## How to update objects
 
+**Warning:** Updating objects with the `replace` command drops all
+parts of the spec not specified in the configuration file.  This
+should not be used with objects whose specs are partially managed
+by the cluster, such as Services of type `LoadBalancer`, where
+the `externalIPs` field is managed independently from the configuration
+file.  Independently managed fields must be copied to the configuration
+file to prevent `replace` from dropping them.
+
 You can use `kubectl replace -f` to update a live object according to a
 configuration file.