This plugin can be used to perform an arbitrary command on multiple channels or contexts. List can be specific to networks, or any context on a separate network. Usage:
To create a /mysay command which does an /allchan for specific channels only, create a User Command (Settings -> Advanced -> User Commands) with the name mysay, and the command:
Now, if you type /mysay goodnight, this message will be sent to the first open instances of #channel1 and #channel2, as well as #bridgechannel on the SpecialNetwork.
To change username on network FreeNode from some other network:
The source code is available in the repo.