Alright.. I'm an attorney and I'm even an attorney for a small municipality where I live so I might be able to help with some input in getting ordinances changed.
First off, rules vary and the methods of changing ordinances can vary from state to state and town to town so probably can't do much in the way of absolutes.
Second, shifting attitudes and getting anything considered seriously is generally easier to accomplish in a small town than a big city (the 15 households that want chickens in a small town could be the deciding votes in the next election.
Okay. So with all that said, do some research. Make sure you know what the current ordinance is and what the process for changing it will be. From there, find other ordinances of local towns that hopefully support your position. Contact your local Town Hall to get on the agenda for the meeting you wish to present your idea to or, alternatively, see if a council person would be interested in spearheading it. If so they can be invaluable in helping you maneuver whatever "politics you may face.
Obviously knowing whatever opposition you may face and their argument (smell, noise, etc.) puts you in a better position to counter it.
Basic negotiating will suggest that you ask for more than you can hope to achieve (flocks of unlimited size regardless of lot size with roosters and hens) which then helps with creating a compromise position.
Seems clear that everyone posting on the forum is plenty familiar with the tenacity that may be required.
Now that I read the post, the suggestions seems obvious so hope someone finds something about it helful.