whenever you make a template change you must save it separately into a group of templates that you can name as you like, you can make multiple groups of templates and make each style use a different group.
the original template will not be modified, the style will use the group template if it exists and the default one when there is no modified version.
the advantage of this concept is whenever you make updates to your forum or style you will always have the original template and the modified one in one place. this makes fixing any potential bug much easier and you can quickly switch between both.
my english is bad and what i wrote might not be clear to some of you. if you are curious enough check the wbb demo and try to modify a template and you will understand what i am trying to say. it will only take 5 minutes.