url redirect with rewrite capability

Assuming that the page is on the same server all you'd need is to change the uri before passing it forward:

when HTTP_REQUEST {

    set host [string tolower [HTTP::host]]
    set uri [string tolower [HTTP::uri]]

    if { $host equals "lion.dev.leo.world.com" and $uri equals "/lookout" } { 
        HTTP::header replace Host "bearcub.dev.leo.world.com"
    }
}

Now, if there's any images, stylesheets ets below /lookout that needs to be loaded you might be better off by using this:

when HTTP_REQUEST {

    set host [string tolower [HTTP::host]]
    set uri [string tolower [HTTP::uri]]

    if { $host equals "lion.dev.leo.world.com" and $uri starts_with "/lookout" }     { 
        HTTP::header replace Host "bearcub.dev.leo.world.com"
    }
}

If the other bearcub.dev.leo.world.com resides on another server you will want to add a pool decision as well:

when HTTP_REQUEST {

    set host [string tolower [HTTP::host]]
    set uri [string tolower [HTTP::uri]]

    if { $host equals "lion.dev.leo.world.com" and $uri starts_with "/lookout" } { 
        HTTP::header replace Host "bearcub.dev.leo.world.com"
        pool bearcub_pool
    }
}

/Patrik