How to alter user's input?
Use the hook_form_FORM_ID_alter and add a custom submit handler.

function example_form_form_id_alter(&amp;$form, &amp;$form_state,$form_id){
  $form['#submit'][] = 'example_form_id_submit',
}

function example_form_id_submit(&amp;$form,&amp;$form_state){
  $form_state['values']['resource_name'] = 'resource_' . $form_state['values']['resource_name'];
}