How to prepend string to existing URI

Let me know if this helps. Set the following iRule. You can also do this using policies as well.

https://support.f5.com/kb/en-us/products/big-ip_ltm/manuals/product/local-traffic-policies-getting-started-12-1-0/1.html

  when HTTP_REQUEST {
   if { [HTTP::uri] eq "/"}{
      HTTP::redirect [string map {/param1&param2 /param3&param1&param2}[HTTP::uri]]
        }
      }

sorry on the eq have that match param. or whatever your landing page will be.

Code

when HTTP_REQUEST { if { [HTTP::uri] eq "/param1&param2"}{ HTTP::redirect [string map {/param1&param2 /param3&param1&param2}[HTTP::uri]] } }

Please test this, I've been using this to match with host and uri.

when HTTP_REQUEST {
    if { [HTTP::host] eq "www.something.com" } 
    {
    if { [HTTP::uri] starts_with "/param1&param2" } {
    HTTP::redirect "/param3&param1&param2" 
    } else {  }
} else {  }
}

when HTTP_REQUEST {
   if { [HTTP::uri] eq "/param1&param2"}{
      HTTP::redirect [string map {/param1&param2 /param3&param1&param2}[HTTP::uri]]
        }
      }