How to change MENU_LOCAL_TASK title for the View and Edit tabs according to content type?
hook_menu() implementations are cached so aren't executed for every page (can you imagine how bad that would be for performance?)

You can use the title callback property from hook_menu() to evaluate a title on each page load, e.g.

$items['node/%node/view']['title callback'] = 'MYMODULE_title_callback';
$items['node/%node/view']['title arguments'] = array(1);

...

function MYMODULE_title_callback($node) {
  if ($node-&gt;type == 'foo') {
    return 'bar';
  }
  else {
    return 'baz';
  }
}