Yes you would require a flash/tune if you added some simple bolt ons. I'm not sure to as if there are any shops near you that have the knowledge to flash your ecu, but there are other options such as mailing your ecu to a well respected company or downloading maps or the Cobb AP. If willing to mail your ecu you should check out AMS's e-flash as well as Work's brainflash. You can also download AMS's e-flash. The Cobb AP is kinda diy, you input the info and it guides you through it. Consider your options. Talk to Mike at RRE or Bryan at GST, they are the mitsu gurus!
They are located in California, but I'm sure they can answer some of the questions you may have and can guide you when and if you decide to mod.