How to override form error message
You can use this twig to theme the status message:

status-messages.html.twig

{#
/**
 * @file
 * Default theme implementation for status messages.
 *
 * Displays status, error, and warning messages, grouped by type.
 *
 * An invisible heading identifies the messages for assistive technology.
 * Sighted users see a colored box. See http://www.w3.org/TR/WCAG-TECHS/H69.html
 * for info.
 *
 * Add an ARIA label to the contentinfo area so that assistive technology
 * user agents will better describe this landmark.
 *
 * Available variables:
 * - message_list: List of messages to be displayed, grouped by type.
 * - status_headings: List of all status types.
 * - display: (optional) May have a value of 'status' or 'error' when only
 *   displaying messages of that specific type.
 * - attributes: HTML attributes for the element, including:
 *   - class: HTML classes.
 *
 * @ingroup themeable
 */
#}
{% for type, messages in message_list %}
  &lt;div role="contentinfo" aria-label="{{ status_headings[type] }}"{{ attributes|without('role', 'aria-label') }}&gt;
    {% if type == 'error' %}
      &lt;div role="alert"&gt;
    {% endif %}
      {% if status_headings[type] %}
        &lt;h2 class="visually-hidden"&gt;{{ status_headings[type] }}&lt;/h2&gt;
      {% endif %}
      {% if messages|length &gt; 1 %}
        &lt;ul&gt;
          {% for message in messages %}
            &lt;li&gt;{{ message }}&lt;/li&gt;
          {% endfor %}
        &lt;/ul&gt;
      {% else %}
        {{ messages|first }}
      {% endif %}
    {% if type == 'error' %}
      &lt;/div&gt;
    {% endif %}
  &lt;/div&gt;
{% endfor %}


I'm not sure, if you can get the form id in this template. But you can try to narrow down the kind of error message and make the modifications to this twig conditional.