My answer to a similar question should give some more info: https://martialarts.stackexchange.com/a/7918/8174
Specifically for your question, it's not bad to mix things up, but you want to prioritize your preferred stance over your switch stance. Many boxing, kickboxing, and MMA coaches won't even have you bother with stance switching. It doesn't do much to confuse or surprise opponents, and is used sparingly (if at all) even at the highest levels. I personally never switch stances in a fight, only screwing around in sparring.
One good time to use your switch stance is when you're put there because of the footwork of a technique. If you throw a jab - overhand right and end up with your right foot forward, great! Now you can throw a big ol' left cross. Or work that right handed jab. You don't want to hang out there too long though. Your opponent's main stance is better than your switch stance.
In summary, the relevance of stance switching has been up for debate forever. Some of the greatest fighters of all time never switch stance. Some do. Work with your coach for what works best for you!