Of course it can, but it is not as simple as you'd hope.
Any noisier horn will be bigger, and won't fit in the same place. I have fitted a pair of Ring horns to mine, each mounted below a headlamp, but it needs the bumper off to do this properly.
Then there is the wiring. I have bought a connector (Ebay) that fits to the loom, so plugs into the loom connector that would normally plug into the original horn. That takes two wires to a relay to activate it when the horn is pressed. Then the relay is fed direct from the battery, through a fuse and the output is split to the two horns.
This took half a day, and the result is not as good as hoped. Previous twin horns have been louder, but finding Fiamms is more difficult.