I find it hilarious that I can exceed the 200 pop cap limit with spoony bards, though! I get around the clothing issues of humans by making them all join military squads. Most just wind up as soldiers anyway.
However, we've (on the forums) long asked for a new noble position called "immigration officer." We could use this noble to set population limits, deny migrants (NO YOU AND YOUR TEN WORTHLESS KIDS CAN'T STAY HERE, YOU DIRTY FISH CLEANER!), and even try to discourage certain professions from arriving. We live in the middle of a barren desert. The only water is our cistern 10 dwarves died trying to secure from the monster-infested caverns. No you can't fish there. You can't fish anywhere. How many times must I tell these people THERE ARE NO FISH IN THE DESERT! Stop migrating here if you want to fish! >.<
The immigration officer/customs man would also be the go-to guy for petition settings. Auto block by race, profession, or maybe numbers (no more than 1 long term resident per 10 dwarves). Or you could just set it to "accept everyone" like I like to. Currently, petitions are actual meetings with your leader (mayor, noble, expedition leader, whoever), so it could either be an expansion of his duties or only default to the leader position in the absence of an immigration officer.