irule to redirect traffic as well as changing the URL

I'd add some logging to see what's happening (and a couple changes to your script). Then check the LTM logs to see what is happening...

when HTTP_REQUEST {
    log local0. "Host: [HTTP::host]"
    if { [string tolower [HTTP::host]] equals "test.abc.com.int.xyz.com"} {
        HTTP::header replace "Host" "www.abc.com"

        log local0. "  URI: [HTTP::uri]"
        switch -glob [string tolower [HTTP::uri]] {
            "/" {
                log local0. "    Setting Pool: XXXX"
                pool XXXX
            }                
            default {
                log local0. "    Setting Pool: XXXX"
                pool YYYY
            }
        }
    }
}