In the good old days, modifying your car was a physical affair. Messing with needle jets. Bolting on goodies. Tweaking stuff here and there. Whilst a lot of this is still true, more and more you'll find people modifying their cars with a cable and a laptop. Essentially, it's now possible to hack your car. Anything from minor functional changes to full-on engine remaps are all possible, but for the DIY-er, it's generally best to stick to the less risky end of things. I'll give you an example. My new VW Tiguan came with a lot of nanny features - things that were put there to appease the lawyers but have no real purpose. With the right piece of kit, I've been able to modify my car to suit my tastes. In this case I've used a Ross-Tech MicroCan. It's a package with a piece of software for my laptop, and a USB cable with an OBD2 connector on the other end. Using their software, I've been able to turn off the seatbelt warning chime, turn off the daytime running lights, make it so that I can have high beams and fog lights on together, alter the behaviour of the trunk release (so it now opens, instead of just unlocking) and a bevvy of other minor tweaks and mods. The interesting thing with VW in particular is that a lot of options for their European models are available, but simply disabled in the onboard system for the US. Using the software, I've been able to re-enable those features.
The other nice thing about this particular piece of kit is that it allows me to see DTC and error codes - the things that turn on check engine lights - and clear them if I want. I can even reprogram my own TPMS monitors when switching from summer to winter wheels and back.
It's the brave new world of car modifying - try it - you'll like it.