Does wanting to wear clothing of the opposite sex mean anything, if you only want to do it sometimes?

No. People can wear whatever they want to. In my opinion, clothing isn't really gendered and experimenting is part of the human condition. Many guys I know wear makeup/more feminine clothing, and plenty of my girl friends wear button ups and more masculine clothing. There isn't anything wrong with dressing how you feel comfortable, and doing so doesn't change your sexuality/gender. Many are highly judgemental of people that change around their presentation, but I don't see anything wrong with it. You rock whatever clothing you want to, my dude/dudette. I'm sure you look amazing no matter how you're presenting.

no it does not mean anything. Society shall define it their own way but you matter and so do your opinions. your opinion about yourself is the only one that matters. It is a free world and not unless there are laws or regulations in your country that do not facilitate wearing opposite sex outfits then you can wear what you want. Who knows? you could be starting a new trend and it could make you famous. Some countries wear opposite sex outfits and that is their culture / tradition. Well if you are comfortable with the outfit then you can wear what you like.