To install a patch simply download the file and overwrite the file with the same name distributed with FreePOPs.
Unofficial plugins are plugins that are not considered stable enough. They are not included in the official distribution but they are available for download.
Since version 0.0.21 there is a special directory in which they should be put. Under Windows it is LUA_UNOFFICIAL (in FreePOPs installation path). Under Unix the right path is usually /usr/share/freepops/lua_unofficial.
You don't need any more to hack config.lua or something, just put the plugin file in the special directory.