No personal experience, but I'm currently planning the same. From what I've read on here, besides the important fact of ensuring both flocks are healthy, it should work. My plans are to move my new flock of chicks into my current coop, in a separated area. I have roosting bars, with a poop board below them. The space under that (4'x12') is not really used. I've build a secure temporary cage under that poop board, and my new chicks will move to that area once they no longer need a heat lamp here in a few weeks. I'll keep them there for another few weeks, so they can intermingle with my current flock, without actually being able to touch each other. Once the chicks have outgrown the temporary cage, I'll open a door in that cage, which will allow the pullets (they will be pullets by then) to come and go as they please, but will be too small for one of my adult ladies to get into. This will give my new pullets some security if needed. Once I'm comfortable that they are all getting along, I'll remove the temporary cage under the poop boards.
I'm doing this because my current coop and run are big enough to accept my new flock with my current flock.