I can tell you how I handle introducing young roosters (cockerels) and it may help, but it also may not be feasible for your situation.
I have introduced a good many cockerels (always fully feathered) as young as 9 weeks to my flocks before without major incident.
I do this by introducing at least 2 new cockerels at a time.
The hens will undoubtedly pick on them (just give them some hidey-holes and cover to hang out behind), but, for me, even with the pecking and squabbling, cockerels always seem to integrate into an established flock better than pullets.
I always try to introduce multiple young cockerels (if I can help it) for a couple reasons-
For one, like I said the hens will pick on them, it's part of upsetting the pecking order by introducing new birds. Having multiple new birds takes the pressure off of just one bird being picked on, plus being introduced to a new flock with a friend helps the newer birds adjust better as well.
Secondly, one of them will usually turn out to be a mean little turd. They start out by chest-bumping then move on to flogging and attacking people. Those go elsewhere.
The problem with only having one cockerel is if he turns out to be a turd, then you have to rehome him and start all over.
If they all turn out good boys, it's pretty easy to find someone with a flock that needs them. Good roosters are hard to come by.
Introducing Multiple cockerels will allow you to weed out the naughty ones and (hopefully) get a good boy.
I've had good luck with this. I hope this helps!
