Roles and permissions

Hi there, our moodle site is version 1.9 on a W2K3 server. My question pertains to roles.

Roles/assign.php line 362

$availableusers = get_recordset_sql('SELECT id, firstname, lastname, email

I want to replace email with username because it's shorter and a more useful identifier in our institution.

Roles/assign.php line 273

if (!$contextusers = get_role_users($roleid, $context, false, 'u.id, u.firstname, u.lastname, ra.hidden')) {

I can remove the e-mail address fine like I have in line 273 above but it's ignoring me when I try to add username or u.username in either of the above lines. I'm thinking I need to edit the get_recordset_sql or the get_roles_users functions. Can anyone tells me where these are located and if my making edits to them will lead me to a world of problems and hurt? If you hadn't guessed, I am not proficient at PHP.

I'd be grateful for any assistance.

Jeff