Answered Customize Manager > user edit window

<?php
$css = '
		 <style>
			/* Country */
	    #x-form-el-modx-user-country, #x-form-el-modx-user-country div, label[for="modx-user-country"] {
	        display: none !important;
	    }
	    /* Gender */
	    #x-form-el-modx-user-gender, label[for="modx-user-gender"], #x-form-el-modx-user-gender input, #x-form-el-modx-user-gender div {
	    	display: none !important;
	    }
	    /* Birthday */
	    #modx-user-dob, label[for="modx-user-dob"], #x-form-el-modx-user-dob input, #x-form-el-modx-user-dob div {
	    	display: none !important;
	    }
    </style>
';

$modx->regClientCSS($css);
 
return '';