custom_blocksy_admin_menu_label.php

<?php
function change_blocksy_menu_label() {
	global $menu;
	foreach($menu as $key=>$one){
		if(isset($one[0]) && $one[0] == "Blocksy"){
			$menu[$key][0] = "My Custom Theme Settings";
			// create custom base64 image with a svg and converter here:
			// https://www.fffuel.co/eeencode/
			// $menu[$key][6] = "data:image/svg+xml;base64,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";
		}
	}
}
add_action( "admin_menu",  "change_blocksy_menu_label" );