Yes, you can separate them (using the right temperature heat gun or oven to soften the glue, yet not melt the whole thing), but it's probably easier just to take the headlight off the car, remove all the bulbs and use a compressed air can to blow air through it to push/circulate the water vapor out.

If you use the off the shelf disposable air cans, make sure not to flip them over, otherwise you'll get some of the liquid from the can. While it does dry quickly, it's just easier to avoid it altogether.

In general, the headlights aren't completely sealed, so water vapor can get in, but by the same token, it can also get out. It's just harder to get it to circulate out.

 

Goobers is right. All of the enclosures, like light housings have to breath otherwise they would break when the air inside expands in the heat or at high altitude or when the air contracts in the cold and/or lower altitudes.

If you actually turn on the headlights (not normal daylight running mode), and drive for any amount of time, that should heat up the air inside the housing and expel the moisture.

But you should check to see if any of the bulbs / twist-in bases are loose or if there is a crack / break in the housing that is allowing more than normal amounts of moisture to get in. Many of us, in all sorts of climates, usually don't see moisture condensing on the inside of the headlight housing.