I've been experimenting with "ridable" NPC characters in OpenSim. I'll have this uploaded soon. We can then ride on a tiger.
You will be able to customize the avatar a little. You can change your hair. You can use a photo editing software to change clothes. It's not really hard but then it's also not very simple. You rez the tiger/avatar and drag and drop new textures on it.
For more information, read metaverse.mitsi.com/secondlife/posts/TigerRider/