With the epic fight mod flame bladed sword, it is initially considered a shield; however I want to configure it to be a sword/light weapon for balance reasons on the server for pvp. I set the type to sword, but it still registers as a heavy weapon instead.

I would double check that you have the resource location correct there. The config does work as expected.

As a note, if you are playing on a server, the config must match on all clients that connect to the server.