Child Styles question

[Infopro]

Not sure I understand you correctly, but You can set the default forum style to be style1, and every other forum clicked change to style2 or style3 or style12 by setting each forum to use its own style and set to override:

Check Style Options for each forum for this section, Style Options.

Custom Style for this Forum

Override Users' Style Choice (If this forum uses a custom style, this will force users with a different style choice to see the forum with the style you specified)