i think you only need to do the seals to perform techniques. Because byakugan isn't really a technique but i bloodline limit. One doesn't need to do the seals, because it's natural for them.
Take episode 61 for instance. You saw hinata and her father training. Neji's father became mad and unleashed his bykugan. he doesn't need a seal for that.
It's the same with Kakashi.