[рони]

kzn,

<div class= "form-group" id="innblock" ng-class="{error: myForm.inn.$invalid}">
            <label> ИНН </label>
            <div>
                <input name="inn" id="iinn" pattern="\d+" ng-model="agent.inn" type= "text" class= "form-control" maxlength="12" placeholder="ИНН" required/>
                <span ng-show="myForm.inn.$dirty && myForm.inn.$invalid" class="help-inline">Введите ИНН</span>
            </div>
        </div>

<script>
    var ell = document.querySelector("div.form-group input[name=inn]");
    ell.setAttribute("maxlength", "10");
</script>