Is it safe to change your stroke when swimming to lose weight?

Any stroke: You will get toned up and leaner looking, but may not lose much weight swimming. Many exercises cause a rise in core temperature, and sweating, etc. These can help reduce weight. The water keeps your temp. Cooler, and you don't sweat, so there is less weight lost. You do burn calories which will help weight loss, but not as much/fast as, for example, playing raquetball hard. Excellent exercise.