I think this could be done by moving some options to the server details window, next to port settings etc.
maybe even rework the perform dialog to put the network specific perform in that same window?
that would give some more control over specific networks.
there should be one place with default settings though to use for servers you didn't set any specific information for.
other would simply be to script your connecting to the networks and set the main + altnick through the /server command ;-]