You can indeed "hack" your car. In fact, ECU flashing is one of the most common upgrades for people who want more power out of their cars because it requires no physical parts.

It's generally done commercially [1][2] though there are attempts at user-configurable software [3]. Now I'm no expert on ECU flashing so these links are just examples.

[1] http://changegears.wordpress.com/2011/05/17/apr-stage-1-ecu-... [2] http://www.velocityfactor.net/scripts/prodview.asp?idproduct... [3] http://www.tactrix.com/index.php?option=com_content&view...