I looked in the code earlier and the default theme is at this moment set as a variable in ubbt.inc.php (if I remember correctly) and at the moment you will have to change the value of that variable to change template.
But it seems that it is a good foundation to provide multiple themes in the future. When the time comes to add new features (for next version?) all that has to be done is to add a new option on the display profile that sets the template, like the skins are selected now.
I for one am looking forward to it, but I'm too lazy to fix it myself, I'd rather wait for the official release, which I hope is not too far into the feature.
