Update Cart’s address ID from plugin
If I am reading you right you are wanting to update the shipping address on the order rather than create a new one. 

You should be able to do that right now:

{% set cart = craft.commerce.carts.cart %}

{% set flashNotice = craft.app.session.getFlash('notice') %}

{% if flashNotice %}
    &lt;div class="bg-blue-500 text-white"&gt;
        &lt;div class="flash container mx-auto px-6 py-4"&gt;
            {{ flashNotice }}
        &lt;/div&gt;
    &lt;/div&gt;
{% endif %}

{% set flashError = craft.app.session.getFlash('error') %}

{% if flashError %}
&lt;div class="bg-red-500 text-white"&gt;
  &lt;div class="flash container mx-auto px-6 py-4"&gt;
    {{ flashError }}
  &lt;/div&gt;
&lt;/div&gt;
{% endif %}


//meat and potatoes:


{{ cart.number }}&lt;br&gt;

Shipping Address ID: {{ cart.shippingAddressId }}

&lt;form method="post"&gt;
  &lt;input type="hidden" name="action" value="commerce/cart/update-cart"/&gt;
  &lt;input type="hidden" name="cartUpdatedNotice" value="The address was updated."&gt;
  {{ redirectInput('shop/address') }}
  {{ csrfInput() }}

  &lt;!-- THIS IS WHAT WILL UPDATE THE ADDRESS VS ADDING A NEW ONE --&gt;
  {% if cart.shippingAddress.id %}
  &lt;input type="hidden" name="shippingAddress[id]" value="{{cart.shippingAddress.id}}"/&gt;
  {% endif %}

  First Name:
  &lt;input name="shippingAddress[firstName]" value="{{cart.shippingAddress.firstName ?? ''}}"/&gt;

  &lt;button type="submit"&gt;Update&lt;/button&gt;
&lt;/form&gt;


As demonstrated above, using an input with name="shippingAddress[id]" with the address ID set as the value will update the address with that ID on the commerce/cart/update-cart controller action just fine.

You would only use name="shippingAddressId" if you wanted to let the user select an existing one.