You can read the fault codes of any ECU controled Vauxhall upto about 1997-1998 using the apaer clip method. However you can NOT change the values.
After that time on newer models, as mentined, the stndards have changed to ODBII, were before all these Bosch and Motronic ECUs etc were only ODBI and they didn't all stick to the rules.
Anyway, to change values you need a TECH1 or TECH2 reader which I belive you can only get if your a VX franciser.
However the good news there are aftermarket ECU readers out there like Haynes, Sykes-Pickvand etc. But they are BOT cheap, saw some for £1000 on the net, and they typicaly go up in price and not down. You only want to buy this stuff if your doing devolment work.
Otherwsie you can replace your std ECU with an aftermarket item and they allow you to connect up a laptop and reprogramme all the settings when on a rolling road.
But with ODBII complient, you can connect up your palm PDA with the correct cable and software (avaible from America) and ou can view the settings and change them. So buy a new car
What as in superchip?
If this is for your V6 I would do the engine modifcations first and THEN buy/install the Unichip. Expensive at £400 but makes best use of your engine modes. A superchip on a normally aspriated engine can be disapointing at times.