Banjo,
Check out the DOTAR website and your local licencing authority website for the latest info.
S3's fall under the 2nd Edition ADR's and any additional rules from your State.
The only ADR's relating to engines are emissions and noise, so your local authority is the place to ring first.
The rule of thumb from DOTAR is that the vehicle must comply with the ADR's on the VIN plate but it is OK to upgrade to a later standard,
Cheers Charlie

