The Human Rights Act 1998
Article 10: Freedom Of Expression
If an employee were to be dismissed because of body piercing that was not thought to be appropriate the Tribunal must take into account the employees right to freedom of expression when deciding whether a dismissal was fair.

The site below makes good reading, especially the Star City case. Very similar to yours but you had the piercing BEFORE the dress code policy.
http://www.cmlawyers.com.au/news/2004/009.html