Switching the wires around won't hurt the speaker. However, it's ideal to keep all your positives and negatives labeled, especially with subs. If the wires are switched on 1 speaker, then the cones will move exactly opposite the normal speaker. This causes sound to get canceled out and your system to not be heard across the lake
(this is especially true in subs placed close to each other). One thing you you shouldn't do however do is mix up positives and negatives from different channels of your amplifier. If you are scared get a voltmeter from home depot and test which wire is which.
Hope you have a good fourth!!!!