Absolutely! I think the best step-parent in the world is the one who loves the spouse, understands that neither parent is perfect, adores the step-kids and knows when to keep their mouth shut

Seriously though, rules in court? Don't disparage the other parent. Ever. Support your spouse, tell the truth and make it crystal clear that parenting their child is *their* job and you would never even think of interfering. In fact the thought hadn't even crossed your mind! That would just be...well..wrong, right?
You'll do just fine. And please, feel free to ask your questions whenever you feel the need.