yes indeed saviola is right. sorry for long response time ive not been so active online recently.
it is not possible to personalize the haxball buttons unless you modify haxwin to use your personal version of haxball that you have cracked that is not so straight forward and i wont do that since it would open up easier possibilities for crackers and cheaters.
haxwin is basically just a browser that runs old version of firefox engine. the only buttons you can modify are the "browser" buttons up and for that you would have to download the source code, edit and compile it yourself. if you are really interested then you can find the source code at
https://github.com/morko/haxwin. it is open source so feel free to do whatever you want with it.