So far, if you need to copy a plugin from one mixer channel to another in FLStudio, it must be done saving the whole mixer channel chain to a file, select another channel and load it.
In FLStudio 9, you have the chance to do it faster:
You could already drop effect presets onto mixer slots. What’s new is that you can drop generators onto mixer tracks, effect presets onto channels or generators, mixer presets onto channels/generators, etc.
Via Image-Line forums.