is it possible to change the gather rate of metal fragments or any desired resource outcome when its in a furnace smelting

ex: from 1 metal ore you get 3 metal frags if you make it 3x

That's out of scope of this plugin.
You'd want to use a plugin like uMod - Quick Smelt by misticos for this but unfortunantly that plugin does not yet support serperation of materials in the config. That is to say, you can make 1 metal ore give you get 3 metal frags, but the same will be true for sulfer and hqm - you can't configure them differently.