How to Hold/Block the messages in PI for particular system

Hi,

I want to know the way of holding/blocking the message in PI for particular system. For other system message flow should happpened normally. My Scenario is,

R3->PI->SRM. For connection between PI and SRM we are using proxy. We are going to upgrade our SRM system. During that time there should not be any message flow to SRM. All the message needs to be blocked in PI. Once the upgrade over, we will restart all the messages.

There are lot more system connected to PI. There should not be any interupt on that, message flow should happned normally for other system except SRM. Only the message going to SRM should be blocked.

I found one way, by locking the user which used in communication channel for SRM system. So all the message will be failed in PI with Authentication error. After upgrade we can restart the message.

Is there any other standard way to hold/block the messages which are going to particular system??

Regards

Baskaran K