Solution
1) Create a custom widget /apps/eaem-cs-smart-crop-rc/dam-tools/userpicker/userpicker.jsp to read the values from config resource /conf/global/settings/dam/eaem-dam-config. It extends otb user picker /libs/granite/ui/components/coral/foundation/form/userpicker using a sling:include, for setting the granite.ui.form.contentpath attribute to read values from config location /conf/global/settings/dam/eaem-dam-config
<%@include file="/libs/granite/ui/global.jsp" %>
<%@page session="false"%>
<%
String CONFIG_RES = "/conf/global/settings/dam/eaem-dam-config";
request.setAttribute("granite.ui.form.contentpath", CONFIG_RES);
%>
"/>
2) Create the tools navigation /apps/cq/core/content/nav/tools/eaem-dam-tools/eaem-dam-config.
3) Create the configuration page /apps/eaem-cs-smart-crop-rc/dam-tools/eaem-dam-config for selecting the group name and save to /conf/global/settings/dam/eaem-dam-config@processAssetsGroup accessed using Tools > Experience AEM > EAEM Configuration or https://author-pxxxxx-exxxxx.adobeaemcloud.com/apps/eaem-cs-restrict-assets-size/dam-tools/eaem-dam-config.html/conf/global/settings/dam/eaem-dam-config
4) Add a render condition script /apps/eaem-cs-smart-crop-rc/smart-crops-render-condition/smart-crops-render-condition.jsp checking if the user is member of group set in /conf/global/settings/dam/eaem-dam-config@processAssetsGroup.