Или так - оптом
<input type='radio' id='free.free'>
<input type='radio' id='simpleid'>
<input type='radio' id='flat.flat'>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<script>
$('input[type="radio"]').each(function (i,item) {
item.id = item.id.replace(/\./g,'_');
alert(item.id)
});
</script>