I can see what the token could be
Code:
&mvt:cattree_categories:customfield_values:customfields:addimg1;
in the Tokens List. But of course, trying to use that token isn't giving me any results so I tried something else. Since this is part of a sub-sub cat display I'm including at the code up to the closing div for the display. What is in bold red is what I need to work:


Code:
<mvt:assign name="l.settings:subcat:id" value=" " />
<mvt:do name="l.result" file="g.Module_Library_DB" value="Category_Load_Code( g.Category_Code, l.settings:current_category )" />
<mvt:do name="l.result" file="g.Module_Library_DB" value="CategoryList_Load_Parent( l.settings:current_category:id, l.settings:sub_categories )" />
<mvt:assign name="l.subcat_count" value="miva_array_elements( l.settings:sub_categories )" />
<mvt:if expr="l.subcat_count GT 0">
<mvt:foreach iterator="subcat" array="sub_categories">
<section>
<p></p>
<ul class="c-form-list o-layout o-layout--wide">
<li class="c-form-list__item o-layout__item u-width-10--m">
<a name="&mvte:subcat:code;"></a>
<h3><strong>&mvte:subcat:name;</strong></h3></li>
<li class="c-form-list__item o-layout__item u-width-2--m">
<h3> <a href="&mvt:category:link;#top"><span class="u-font-small u-icon-chevron-up"></span>
<strong class="u-color-red">Back to top</strong></a></h3></li>
</ul>
</section>
<mvt:comment>tweaked with Ted's help</mvt:comment>

<mvt:assign name="l.settings:myProducts" value="0" />
<mvt:do name="l.doit" file="g.Module_Library_DB" value="Runtime_ProductList_Load_Offset_Category( l.settings:subcat:id, g.Offset, l.settings:null, g.NextOffset, l.settings:myProducts )" />
<section class="o-layout o-layout--row--l o-layout--wide">
<div class="o-layout__item u-width-3--l">
<mvt:do file="g.Module_Root $ '/modules/component/cmp-cssui-cattitle.mvc'" name="l.success" value="CSSUI_CatTitle_Load(l.settings:subcat:id, l.settings:subcat:title_image)" />
<img src="&mvt:subcat:title_image:image;" alt="&mvte:subcat:name;">
<mvt:item name="customfields" param="Read_Category_Code( l.settings:subcat:code, 'altimg1', l.settings:altimg1 )" />
&mvte:altimg1;
</div>