HTML validation constraints - setCustomValidity and novalidate

I'm struggling with the HTML5 native form validation. My understanding from Client-side form validation is you can manually set the validity state of an element with setCustomValidity(). However, this doesn't seem to override any native validation.

For example, if I have a field with required="required" and that field is empty, it is invalid (as expected). If I call setCustomValidity('') on that field, I would expect it to override and set it as valid, but that doesn't happen.

I then thought I could dynamically add novalidate to the field when I want the field to be valid, but if I call checkValidity() after adding novalidate it still returns false. It seems novalidate is only good for allowing the form to be submitted regardless of the fields validity, but the field is still considered :invalid.

Am I missing something, or is this the expected behavior? Also, is there anyway to override any default validations and manually set a field's state to :valid? I would expect something like setValidity(true|false) to be available in the constraint validation API.

A little more context:

I need to toggle a fields constraints based on another fields value. For example, let's say I have the following markup:

<form>
    <div>Has Document?</div>
    <input id="hasDocumentYes" type="radio" value="1" required="required"><label for="hasDocumentYes">Yes</label>
    <input id="hasDocumentNo" type="radio" value="0" required="required"><label for="hasDocumentNo">No</label>

    <label for="documentFile">Document File</label>
    <input id="documentFile" type="file">

    <label for="documentType">Document Types<label>
    <select id="documentType"></select>
</form>

If the user selects "Yes" for "Has Document?", then I want documentFile and documentType to be required. The only working solution I have so far is to dynamically add the required="required" attribute to documentFile and documentType when "Yes" is selected, and then manually call checkValidity().

This works, but it's not ideal. I have lots of these conditional validations that are not always as simple as just required or not required.

Here is the simplified example of the JS I've tried:

// if #documentFile has a required attribute and is empty, the :invalid styles
// are stilled applied after calling setCustomValidity with an empty string
$('#documentFile')[0].setCustomValidity('');

// adding a novalidate dynamically and calling checkValidity() still returns
// false if the field has the required attribute and is empty
$('#documentFile').attr('novalidate', 'novalidate');
$('#documentFile')[0].checkValidity(''); // returns false