It is possible, yes, using the messages option to jQuery Validate.
$('form').validate({
rules: {
cmp_email: {
minlength: 5,
required: true,
email: true,
remote: {
url: "\/client\/check-email",
type: "post"
}
},
},
messages: {
cmp_email: {
remote: "This email already exists"
}
}
});