É exatamente isso que o texto do Combat Style Master diz:
You can switch your style as a free action. At the start of combat, pick one of your styles. You start the combat in that style, even in the surprise round.
Sobre a definição de uma ação gratuita :
Free actions consume a very small amount of time and effort. You can perform one or more free actions while taking another action normally.
Observe que o número de ações gratuitas disponíveis é limitado pelo seu GM.
However, there are reasonable limits on what you can really do for free, as decided by the GM.