Nope has to be declared to DVLA...
http://dvlaguide.co.uk/index.php/dvl...ange_tax_disc/
...
"If the Fuel Type or Engine Size Has Changed
For changes to the fuel type or engine size (cylinder capacity), which needs a lower rate of vehicle tax to be paid, you must provide documentary evidence of the change. This can be the receipt for the new engine, written evidence from the manufacturer, insurance company or garage that carried out the change."
I presume and am pretty sure it would change the amount of tax you pay as obviously car will be producing different emissions. Either way it has to be declared to DVLA.
Obviously has to be insured as 2.0 turbo as well, I believe it can actually void your insurance too if not declared to DVLA (we contacted Adrian Flux on the ZR site and asked this question a while back)