Use presets to change a form
If the property name has spaces or special characters, there is no need to quote it (and it looks more clear):

var obj = {
    preset_a: {
        input: {
            field_a: "value",
            field_b: "value",
        }
        "i need quotes": "value"
    }
}


I tried to improve the function a little bit. I did it on the fly so i'm pretty sure that something could be wrong. Check it out:

function applyPresets(preset){
    // as Quill said, the return(s) statement has more sense at the top of the method
    if( typeof obj[preset] == 'undefined' ){
        alert('Preset [ ' + preset + ' ] not found!');        
        return;
    }
    for( var i in obj[preset] ){
        if( obj[preset].hasOwnProperty(i) ) { // .hasOwnProperty() can be used to determine whether an object has the specified property as a direct property of that object, very useful here
            $.each(obj[preset][i], function(k, v){ // since the code seems very similar we can improve it avoiding more loops
                if( i == 'radio' ){ // if the code below doesn't match, we will need this `if`
                    $('fieldset#' + k + ' &gt; input[type="radio"]').val(v);
                }
                else $(i + '#' + k).val(v); // while they match we don't need more code
            });
        }
    }
    submitSettings();
}


In summary: We use an in loop through the obj[preset] object. This gives us the name of i, so we can easily discard undefined(s) thanks to the .hasOwnProperty() method. The last step is avoid the loops. The syntax is quite the same so we can work inside only one .each() loop. If the selector changes we can always use the lovely if statement.

I made a jsFiddle with the code if you want to see it clearly.