Here's how I solve it:
File edited: parent-children.php
Add a condition to filter the ChildLookupField and apply a custom title to it. In my case, the ChildLookupField is "parentid".
/* process requested operation */
switch($Operation){
/************************************************/
case 'show-children':
/* populate HTML and JS content with children tabs */
$tabLabels = $tabPanels = $tabLoaders = '';
foreach($userPCConfig as $ChildTable => $childLookups){
foreach($childLookups as $ChildLookupField => $childConfig){
if($childConfig['parent-table'] == $ParentTable){
$TableIcon = ($childConfig['table-icon'] ? "<img src=\"{$childConfig['table-icon']}\" border=\"0\" />" : '');
if($ChildLookupField != "parentid"){
$tabLabels .= sprintf('<li%s><a href="#panel_%s-%s" id="tab_%s-%s" data-toggle="tab">%s%s</a></li>' . "\n\t\t\t\t\t",($tabLabels ? '' : ' class="active"'), $ChildTable, $ChildLookupField, $ChildTable, $ChildLookupField, $TableIcon, $childConfig['tab-label']);
}else{
$tabLabels .= sprintf('<li%s><a href="#panel_%s-%s" id="tab_%s-%s" data-toggle="tab">%sBOM Item</a></li>' . "\n\t\t\t\t\t",($tabLabels ? '' : ' class="active"'), $ChildTable, $ChildLookupField, $ChildTable, $ChildLookupField, $TableIcon);
}
$tabPanels .= sprintf('<div id="panel_%s-%s" class="tab-pane%s"><img src="loading.gif" align="top" />%s</div>' . "\n\t\t\t\t", $ChildTable, $ChildLookupField, ($tabPanels ? '' : ' active'), $Translation['Loading ...']);
$tabLoaders .= sprintf('post("parent-children.php", { ChildTable: "%s", ChildLookupField: "%s", SelectedID: "%s", Page: 1, SortBy: "", SortDirection: "", Operation: "get-records" }, "panel_%s-%s");' . "\n\t\t\t\t", $ChildTable, $ChildLookupField, addslashes($SelectedID), $ChildTable, $ChildLookupField);
}
}
}