With iRule V4.x, Can I add or modify cookie ?

You can insert cookies to requests using the header insert attribute on a pool. Example:

pool cookie_machine {
   header insert "Cookie: kind=blueberry"
   member 1.2.3.4:80
}

There is no way how to modify existing cookie. You cannot insert arbitrary Set-Cookie statements into responses, only loadbalancing cookies needed for cookie based persistence.