gistfile1.txt

$(".btn").click(function(e){
    e.preventDefault();
    novo_link = 'http://www.site.com.br/site';
    $(this).text("Novo Texto do btn").attr({
        class: "btn-add",
        href: "novo_link"
    });
    window.location = novo_link;
});

Ou

$(".btn").click(function(e){
    e.preventDefault();
    $(this).text("Novo Texto do btn").attr({
        class: "btn-add",
        href: "novo_link"
    });
    window.location = $(this).attr('href');
});