iRule rewrite | URL hiding

The F5 is giving me an error

can you try something like this?

e.g.

root@(ve11-8)(cfg-sync In Sync)(Active)(/Common)(tmos) list ltm rule myrule
ltm rule myrule {
    when HTTP_REQUEST {
  log local0. "BEFORE: client:[IP::client_addr]:[TCP::client_port] host:[HTTP::host] uri:[HTTP::uri]"
  if { [HTTP::host] eq "www.mysite.com" and [HTTP::uri] starts_with "/help/site1/" } {
    HTTP::header replace Host "news.bizsite.com:8080"
    HTTP::uri [string map {"/help/site1/" "/ehelp/microsites/"} [HTTP::uri]]
    log local0. "AFTER: client:[IP::client_addr]:[TCP::client_port] host:[HTTP::host] uri:[HTTP::uri]"
  }
}
}

Do I need to put the iRule I created on top of the Irule list associated with the virtual server in order for it to be read by F5?

Stacking iRules: A Modular Approach by Deb Allen

as I've mentioned I have little room for error as this is Prod.

i think it is better if you can test using trial or evaluation license before applying to production.

Trial Software Site