The popup's that come with mIRC will only op/voice etc. the first selected 3.

If you want to be able to do more, then you'll need to do a bit of scripting. At this point, it starts to be called a 'mass' action, which is easy to abuse.

You also have to take in to consideration how many modes you can do in one command, as is limited by the server. See the $modespl identifier, which is filled with the 'MODES' argument on the 005 line.

If you want help writing such a script, let us know.