So anytime the designer makes a change to the structure of the application, where HTML element changes are required, do they send you a request so you can change it?

It seems odd to only allow the "designer" to manipulate properties of elements and not the elements themselves. If they are allowed to modify DOM elements then in the React world, that is manipulating JS. For us the important separation is at the component level, which includes everything that component needs to render and function (HTML, CSS, JS).