So let me ask this… Is adding several hens to a flock easier than adding several pullets?
How old will the pullets be? If they are pretty young I'd suggest a different approach than if they are Point Of Lay (POL). Others have discussed older hens. Also how much space you have in the coop, in the run (if you have one), and when they have access to would pay a part in my strategy.
If they are three months old or younger I'd set up a separate "grow-out pen" where they can see the adults but be kept inside until they learn to return there at night to sleep. Once I'm comfortable they will return there to sleep I'd let them free range with the adults during the day but sleep separately at night. Then, when they hit POL, say 16 weeks of age, I'd wait until dark and lock the pullets in the main coop. Of course I already have the facilities to do this so that makes it easier for me. I typically move mine into the main coop at 12 weeks, not wait until 16, but 16 would be my deadline because I'd want them in there when they start to lay.
I do this regularly. Often I only have to move them once and they make the move. Sometimes I have to move them a few nights before they catch on. I lock the grow-out coop so they cannot go to sleep there and I think how my coops and runs are configured play a part.
How big your main coop is and how it is laid out would also affect my decision on mature laying hens or immature pullets. Mature laying hens should immediately work their way into the pecking order. As Centrarchid said, that can lead to rougher battles. "Can" doesn't always mean "will", but rougher battles are possible and more likely with mature hens. With my method and facilities I practically never see fights when adding pullets.
There can be exceptions but in general my immature pullets do not stand up to mature hens until they start to lay. Until then they avoid the adults as much as they can. This means during the day and especially at night on the roosts. In my opinion if you add immature pullets you need more room in the coop. Regardless of how old the new ones are I'd be down there at the break of day to open the pop door until I determined you won't have a massacre. With my set-up and methods that's usually once or twice. Your results could be different.
I'll specifically mention roosts. My brooder-raised immature pullets almost never sleep on the main roosts with the adults until they start to lay, even with a lot of extra room. If they try they will probably be pecked or worse so they look for a safer place to sleep. As long as it is not in my nests and predator-proof I don't care where they sleep. I integrate different broods of chicks every year. To avoid them sleeping in the nests I put up a separate roost lower than the main roost, separated from the main roost horizontally by a few feet, and higher than the nests. I don't know if you will have a problem with them sleeping in the nests or not, your coop configuration will be different from mine. It does happen though, so be prepared.
As always there are different ways to go about this. Each method has its benefits and risks. I'm not going to say that one method is better than another, just different. Good luck however you decide.