Your best bet would be a Power Commander 5, or a Two Bros Juice Box. These are a plug in system that allows you to play with the fuel map. To my knowledge, there is no replacement ECU for the 400R.
You will not get a huge boost in power, unfortunately there is alot more work required to get more power. Apart from a new exhaust, that only leaves extensive work to the engine that will be extemely costly for little gain.
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