Thanks, @phoneboy , you're right!
Since Studio doesn't allow creation of that override, you'll need to use the Community SDK to do it. And you'll also need to create the endpoint XML file, if you want the override to show up in Studio after creation. You'd need these two files:
/res/controllers/theme-lib.profile-card.ftl:
<#compress>
<#setting number_format="0.######"/>
<#include "theme-lib.common-functions.ftl" />
<#assign userId = getRequestField("userId", "-1", true)?number />
<#if userId gt 0 && validEndpointRequest(false, true, false)>
<#assign userQry = "SELECT login, view_href, rank.name, rank.color, avatar.profile FROM users WHERE id='${userId}'" />
<#assign userProfileData = executeLiQLQuery(userQry) />
<#if userProfileData?size gt 0>
<#assign userProfileData = userProfileData[0] />
</#if>
<div class="lia-message-author-avatar lia-component-author-avatar">
<div class="UserAvatar lia-user-avatar lia-component-common-widget-user-avatar">
<span class="UserAvatar lia-link-navigation">
<img class="lia-user-avatar-message" title="${(userProfileData.login)!""}" alt="${(userProfileData.login)!""}" src="${(userProfileData.avatar.profile)!""}" />
</span>
</div>
</div>
<div class="user-info">
<div class="mini-profile-author">${(userProfileData.login)!""}</div>
<div class="mini-profile-rank">${(userProfileData.rank.name)!""}</div>
</div>
<div class="links-area">
<a href="${(userProfileData.view_href)!""}" class="profile-link">${text.format("custom.mini.profile.view.link")} <i class="lia-fa lia-fa-angle-right"></i></a>
</div>
</#if>
</#compress>
/res/endpoints/theme-lib.profile-card.endpoint.xml:
<endpoint version="1.0.0" key="theme-lib.profile-card" feature="custom.communitythemes.support">
<model/>
<view type="freemarker" contenttype="text/html" macro="false"/>
<controller id="basic" path="/theme-lib.profile-card"/>
</endpoint>
I tested this out in a sandbox, and I see this in Studio:
