Maybe you're the only one being bothered by the red icons, but you're definitely not alone regarding new 'protections'.

Currently you can use a dll to change the Status icon when mIRC starts. For example,
  • On *:start:{
    var %cmd = dll sz.dll SetIcon status window > status.ico
    server my.first.server
    %cmd
    server -m my.second.server
    %cmd
    server -m my.third.server
    %cmd
    }

    (tested on Win98se with v6.12)
This command changes only the window icon, and the Switchbar icon remains intact. I don't think you can change it with a single command unless you get or write a script with a custom Switchbar.

If you eventually decide to stick to 6.03, an editable yet exploitable version, this post might help.