How to Change YouTube Rollers on Each Video

I can download and play Youtube Video through the iFrame API, but I cannot figure out how to change the player parameter for the second video. I don't want any controls on the first video, and then when the user clicks on my custom Play Video, I want to play the second video with a control bar. I can set playerVars to initialize the player, but I don't know how to change it when the player is already loaded. Any ideas?

Many thanks.

var player;
function onYouTubeIframeAPIReady() {
    player = new YT.Player('player', {
        videoId: 'M7lc1UVf-VE',
        playerVars: { 'autoplay': 1, 'controls': 0 },
        events: {
            'onReady': onPlayerReady,
            'onPlaybackQualityChange': onPlayerPlaybackQualityChange,
            'onStateChange': onPlayerStateChange,
            'onError': onPlayerError
        }
    });
}

function onPlayerReady {
    var $btn = '<button id="play">Play Button</button>';
    $('#nav').prepend($btn);
    $('#play').click(function() {
        player.loadVideoByUrl('http://youtu.be/GBHxL-LXJbs?controls=1');
    });
}