Not able to properly alter the forms

Issue Summary

The problem is that on every submit function for the form you use , you have drupal_goto and that prevents the other modules to execute their submit functions if they altered the form. The way it is made in drupal 6 is to add $form['#validate'] when you build the form and this way all the submit functions added to the form will be executed and you will get to the desired place. Also if some module wants to change the place the form will redirecte it can directly edit the $form['#redirect'] :

http://api.drupal.org/api/file/developer/topics/forms_api.html/6 :
To determine where the user should be sent after the form is processed, the _submit function can place a path or URL in $form_state['redirect'] which will be the target of a drupal_goto; every form is redirected after a submit. If you store nothing in $form_state['redirect'], the form will simply be redirected to itself after a submit. It is polite to use drupal_set_message() to explain to the user that the submission was successful.