A few weeks ago my colleague informed me you can customize the NetScaler Gateway portal by using rewrite/response policies to edit the HTML code footer area . You can use this option to make important announcements or a disclaimer. In this blog post I will show you how to do this.
NetScaler management GUI
For the non-command line guru’s we configure this first via the management GUI.
Go to AppExpert -> Rewrite -> Actions -> Add
Create a new Rewrite action as seen in the example screenshot:

- Name: Fill in a policy name
- Type: INSERT_BEFORE_ALL
- Expression to choose target location: HTTP.RES.BODY(120000).SET_TEXT_MODE(IGNORECASE)
- Expression (example): Download link
- Pattern: box_view.prepare_view();
- OK (Close)
Next, we make a Rewrite Policy.
Go to AppExpert -> Rewrite -> Policies -> Add

- Name: Fill in a name
- Action: Select the previous created Action
- Undefined-Result Action: -Global-undefined-result-action-
- Expression: HTTP.REQ.URL.CONTAINS(\”gateway_login_view.js\”)
- OK (Close)
Next, we add the newly created Rewrite Policy to our NetScaler Gateway vServer.
Edit your vServer and add a Rewrite/Response policy.

And here is the end result:
Command-line
Here are the command-line options to configure this.
WordPress messes up the output. Here is the download link example.
Credits: http://tech.stelte.nl