Evgeniy2019123,
<!DOCTYPE html>
<html>
<head>
<title>Untitled</title>
<meta charset="utf-8">
<style type="text/css">
</style>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.12.4/jquery.min.js"></script>
<script>
$(function() {
var n = true;
$('#start_change').click(function(){
$('.changeable').prop('readonly', n = !n);
});
});
</script>
</head>
<body>
<button id="start_change">click</button>
<input type="text" class="changeable" readonly="readonly">
<input type="text" class="changeable" readonly="readonly">
<input type="text" class="changeable" readonly="readonly">
<input type="text" class="changeable" readonly="readonly">
<input type="text" class="changeable" readonly="readonly">
</body>
</html>