Is it possible to extend/upgrade media decoders? As I am very happy with the internal player for music I would like to keep it. Unfortunately it does not support a certain codec: flac. Is it possible to upgrade the player so it can decode flac?, or do I have to switch to another player?
Core Media Formats table from Official Android Developer site states that FLAC Decoder is integrated and available by default in Android 3.1 and newer versions. 

So if you want FLAC decoder for your stock media player, you either need to get your device upgraded to ICS(4.0) OR you can switch to another media player (such as andLess or Winamp) that has its own playback libraries to support multiple codec formats including FLAC.