Can Bus What Do We All Know?

Right before anyone says anything yes i have searched the internet but information tends to be scattered around. I drive a 4.3 V8 Lexus Gs and to cut fuel cost decided to buy the new Ka to share with the wife. only picked car up about 3 days ago already going back to ford its 09 with under 4000 miles on the clock. have the fiat milage flash problem, i read that this is miscommunication with the can bus system.

right to the point what i really wanted to know is how much is controlled by the can bus system now i would like to add alarm central locking and power windows to the ka. but i read that this all needs to be linked into the system. As a customer can i request that the PIDs for security and things like displaying the radio information on the gauges to be unlocked or do dealers get funny about unlocking things that you should have payed extra for when buying.

It just seems a shame that more and more cars are no using faster computer system when it is clearly not needed i mean i learnt to drive in an escort 4 years ago, Crashed the first one 3 days after test and then got another one. That car worked fine and all it had was one computer controlling a single fuel injector so why do companies now find the urge to mess things around. I mean i love fords how they are cheap and you can take them apart and rebuild with a socket set and a 10 pound gift voucher from halfords. Do they really need computers than stop even the smallest things like adding HID lights with ought spending large amounts of money on extra adaptors.

Sorry random rant are there any devices out there to allow us to control the can bus system and what is activated or is it solely dealer controlled, if so this is the beginning of the end for the home mechanic.

if there are any gurus out there any information will be appreciated use seems my 320hp v8 is easier to take apart and fix than a little cheap 1.2 polish half fiat Ka