Upgrade Compatibility

Signed-off-by: Zixuan Liu <[email protected]>

Author: nodece

Diff for: pip/pip-398.md

@@ -212,12 +212,22 @@ Both write and read operations require the necessary permissions, which already
 
 ## Upgrade
 
-None.
+The existing subscription with `replicateSubscriptionSate=false`,the broker will use the policy from the topic or namespace level.
+
+New subscriptions will be followed as usual.
 
 ## Downgrade / Rollback
 
-If the broker is downgrade, users will need to ensure that the consumer-level configuration is re-enabled to maintain
-the correct replication behavior.
+If the broker is downgrade, users will need to ensure that the subscription replication configuration is re-enabled to maintain
+the correct replication behavior by the admin CLI or API:
+- CLI:
+  ```shell
+  pulsar-admin topics set-replicated-subscription-status <tenant>/<namespace>/<topic> -s <subName> -e
+  ```
+- API:
+  ```java
+  admin.topics().setReplicatedSubscriptionStatus(topic, subName, true);
+  ```
 
 ## Pulsar Geo-Replication Upgrade & Downgrade/Rollback Considerations