Bi Roix version 0.10.0 support modifications. Just add jar files in the mod directory  
to change almost every game element. Any PNG picture  or OGG sound in `desktop-release.jar` can be replace by files from a mod. Even you can modify BeanShell scripts (.bsh) to change some behaviors. A jar file is basically a ZIP file with another extension.

In Windows the mod directory is %userprofile%\documents\biroix\mods. In Mac and Linux is $HOME/documents/biroix/mods. In instance, download and copy 01_gnu_pieces.jar in your mod directory to change the piece set in any game level.

You can put multiple mods in your mod directory. The mods will be apply sorted by name. So 04_mymod.jar will be applied before 05_mymod.jar and so on.