You can add
add_filter('breadcrumb_theme_args', 'breadcrumb_theme_args_20200203');
function breadcrumb_theme_args_20200203($themes){
// Enabled
$themes['theme_custom']= array('name'=>'Theme Custom','thumb'=> breadcrumbAddon_plugin_url.'assets/admin/images/theme-custom.png');
//Disabled
$themes['theme_custom2']= array('name'=>'Theme Custom2','thumb'=> breadcrumbAddon_plugin_url.'assets/admin/images/theme-custom.png', 'disabled'=>true, 'pro_msg'=>'Only in pro');
return $themes;
}