Can i bring a webpage (node) up/down using irules?

I assume you're looking for a way to allow someone who has admin rights to the web server to take down a node.

Suggestions:

1. Have the web admin stop the web site instance. Assuming that you have configured monitors for the pool this will mark the node down.
2. If the web server relies on its own file repository (vs. a file server that's used for multiple nodes) you can create a monitor that verifies specific content on the web server. For instance, the web admin could rename a specific file, or change its content and the monitor could mark the node accordingly.