I've got the 1.6S. Don't mod the poor thing, they're quick enough for the engine size.
If you need to make it sound a bit more cheeky, whack in an air filter and change the exhaust - but you'll be looking at something like £200 more on your premiums, because you've gone from having a "sensible" car to something sporty. The exhaust change alone will make a lot of insurers just say "no" to you, to be honest.
Assuming you're in the sub-18 bracket.