I was wondering how to change the fields which a backend user can edit by clicking on “User John Doe” in the backend.
It’s simple.
Just create a new module (or use an existing one like mycompany_mycustomerlocal) and under dca/tl_user.php with the following palette definition:
$GLOBALS['TL_DCA']['tl_user']['palettes']['login'] = '{name_legend},username,' . 'name,email;{password_legend},password';
That is it.
I found this by digging into the code a system/modules/core/modules/ModuleUser.php:52