Is it possible to hook_form_alter by path?
I think you should use  $_SERVER['HTTP_HOST'] . request_uri();

This will give you the complete path. 

So your code should be 

function MYMODULE_form_alter(&amp;$form, &amp;$form_state, $form_id, $host) {
  $host = $_SERVER['HTTP_HOST'] . request_uri();
  if ($host == "m.local.dev/donate" or  $host == "m.live.com/donate") {
  $form['submitted']['donation']['amount']['#title'] = t('My new title');
   }
}