Is it possible to change the attributes of an object after processing in the underlying template?

Question

Drupal

Hello!
There is a site on Drupal 8, and downgraded Twig 1.3, you need to add a class and a couple of data-attributes to the image displayed in a certain block.

Output code with debug enabled:

<a class="case-box__link-cover link-inline" href="#case_314">

<!-- THEME DEBUG -->
<!-- THEME HOOK: 'field' -->
<!-- FILE NAME SUGGESTIONS:
   * field--node--field-case-cover--case.html.twig
   * field--node--field-case-cover.html.twig
   * field--node--case.html.twig
   * field--field-case-cover.html.twig
   x field--image.html.twig
   * field.html.twig
-->
<!-- BEGIN OUTPUT from 'themes/salesvp/templates/field--image.html.twig' -->
  
<!-- THEME DEBUG -->
<!-- THEME HOOK: 'image_formatter' -->
<!-- BEGIN OUTPUT from 'core/modules/image/templates/image-formatter.html.twig' -->
  
<!-- THEME DEBUG -->
<!-- THEME HOOK: 'image_style' -->
<!-- BEGIN OUTPUT from 'core/modules/image/templates/image-style.html.twig' -->

<!-- THEME DEBUG -->
<!-- THEME HOOK: 'image' -->
<!-- BEGIN OUTPUT from 'themes/bootstrap/templates/system/image.html.twig' -->
<img src="/sites/default/files/styles/standartnyi_720x405_/public/covers/unihim_prew_img.jpg" class="img-responsive" width="720" height="405" alt="" typeof="foaf:Image">
<!-- END OUTPUT from 'themes/bootstrap/templates/system/image.html.twig' -->

<!-- END OUTPUT from 'core/modules/image/templates/image-style.html.twig' -->

<!-- END OUTPUT from 'core/modules/image/templates/image-formatter.html.twig' -->

<!-- END OUTPUT from 'themes/salesvp/templates/field--image.html.twig' -->

</a>

How to do it? I tried like this:
1) I see that "field--image.html.twig" is used for output. I created a more precise one - "field--field-case-cover.html.twig", and put the modified code of the original template into it:

{% for item in items %}
  {# Попытался добавить класс и свой атрибут #}
  {{ item.attributes.addClass('responsively-lazy') }}
  {{ item.attributes.setAttribute('srcset', 'data:image/gif;base64,R0lGODdhAQABAPAAACwsLAAAACwAAAAAAQABAAACAkQBADs=') }}

  {# Ну и вывод #}
  {{ item.content }}
{% endfor %}

In response, my attributes are displayed as a string + the original image itself

Conclusion:

<a class="case-box__link-cover link-inline" href="#case_314">
      
<!-- THEME DEBUG -->
<!-- THEME HOOK: 'field' -->
<!-- FILE NAME SUGGESTIONS:
   * field--node--field-case-cover--case.html.twig
   * field--node--field-case-cover.html.twig
   * field--node--case.html.twig
   x field--field-case-cover.html.twig
   * field--image.html.twig
   * field.html.twig
-->
<!-- BEGIN OUTPUT from 'themes/salesvp/templates/field--field-case-cover.html.twig' -->
   class="responsively-lazy"
   class="responsively-lazy" srcset="data:image/gif;base64,R0lGODdhAQABAPAAACwsLAAAACwAAAAAAQABAAACAkQBADs="
  
<!-- THEME DEBUG -->
<!-- THEME HOOK: 'image_formatter' -->
<!-- BEGIN OUTPUT from 'core/modules/image/templates/image-formatter.html.twig' -->
  
<!-- THEME DEBUG -->
<!-- THEME HOOK: 'image_style' -->
<!-- BEGIN OUTPUT from 'core/modules/image/templates/image-style.html.twig' -->

<!-- THEME DEBUG -->
<!-- THEME HOOK: 'image' -->
<!-- BEGIN OUTPUT from 'themes/bootstrap/templates/system/image.html.twig' -->
<img src="/sites/default/files/styles/standartnyi_720x405_/public/covers/unihim_prew_img.jpg" width="720" height="405" alt="" typeof="foaf:Image" class="img-responsive">

<!-- END OUTPUT from 'themes/bootstrap/templates/system/image.html.twig' -->

<!-- END OUTPUT from 'core/modules/image/templates/image-style.html.twig' -->

<!-- END OUTPUT from 'core/modules/image/templates/image-formatter.html.twig' -->

<!-- END OUTPUT from 'themes/salesvp/templates/field--field-case-cover.html.twig' -->

</a>

I see that the "rendering" of the img entity itself takes place in the "themes/bootstrap/templates/system/image.html.twig" template, along the chain from my custom template, bypassing a few more files.
Tell me, please, can I change the attributes of an entity that was prepared by underlying templates from my field template?