It will disrupt the pecking order, but they should be able to sort it out quickly.
I have two SLW who are big bullies since they were young - they even bullied my poor Dark Brahma rooster. Once I added another rooster, he became the head honcho, and put the two bullies in their place - they went from top to bottom of the pecking order in no time. Some months later I had to get rid of this new rooster, and the pecking order was rearranged - the two bullies climbed up again, fighting the gone rooster's favorites for the prime spot. But it all happened within a week, with very few feathers lost, just a lot of screming. You should be fine.
In my experience, if chickens (hens and roosters) have enough space, they can sort things out pretty quickly and without too much violence ;-).