Dynamic Material

I'm trying to add an object which can dynamicly change it's texture. My object is named "Planet" so I named the material BASE.Planet and the texture BASE.Planet.png. I then used

function Planet::onAdd(%this, %obj)
{
	%obj.setSkinName("Splotchy");
}

to set the texture to Splotchy.Planet.png, but nothing changed and it didn't report an error.
What am I doing wrong?

Edit:
The first texture works fine, but when I change it nothing happens.