docs: Document tag replacement behaviour for Zendesk updates (#3850)

Co-authored-by: Kartik Balasubramanian <22399046+HumanistSerif@users.noreply.github.com>

Author: jabbson

docs/integrations/builtin/app-nodes/n8n-nodes-base.zendesk.md

@@ -46,6 +46,18 @@ Refer to [Zendesk credentials](/integrations/builtin/credentials/zendesk.md) for
     * Get data related to the organization
     * Update a organization
 
+/// warning | Tag Replacement Behavior
+When using the Zendesk node's "Update Ticket" operation and specifying the `Tag Names or IDs` field, the entire list of tags on the ticket **will be replaced**. Any tags not included in the update will be removed from the ticket due to how the Zendesk API processes tag updates by default.
+
+**To avoid accidental tag removal:**
+
+- First retrieve the ticket's tags and merge them with your new tags before updating.
+- Alternatively, use the HTTP Request node with Zendesk's `additional_tags` property to add tags without removing existing ones.
+- You can also call the ticket's `/tags` endpoint to add tags without replacing existing ones ([Zendesk tags endpoint documentation](https://developer.zendesk.com/api-reference/ticketing/ticket-management/tags/)).
+
+See the official documentation for details: [Adding tags to tickets without overwriting existing tags](https://developer.zendesk.com/documentation/ticketing/managing-tickets/adding-tags-to-tickets-without-overwriting-existing-tags/).
+///
+
 ## Templates and examples
 
 <!-- see https://www.notion.so/n8n/Pull-in-templates-for-the-integrations-pages-37c716837b804d30a33b47475f6e3780 -->