Removing a functionality from a slot has often a dual impact: on html presentation and on php code. For example to remove a delete functionality, you've both to remove a delete button from html and not allow to execute the delete code section. It's very important to also not allow code execution because an expert user may post a forged form and delete what he/she's not allowed to delete.

Example PHP script:
<?php

function core_test_()
{
    global $_obweb;

    $user =& new user();
    /* showing delete language button depends on having
     * dellang operation (just an example, not a real operation)
     */
    $show["dellang"]=$user->has(1, "dellang");
    /* checking for dellang button push AND if it's allowed to push it */
    if ($_GET["action"]=="dellang" AND $show["dellang"]) {
        /* delete language code */
    }
    /* pass show array to Smarty slot template, so we can hide delete
     * button if needed
     */
    $_obweb->smslot->assign(array("show" => $show));
}
?>

Example HTML Smarty template:
{{if $show.dellang}}
<a href="index.php?page=core_test&action=delete">delete</a>
{{/if}}