QF - display the same form with changed select box

Hi! How can I change a Form after a Button was pressed? It seems (and was discussed here before) that the form is build before Actions are processed. But I want to change the selectable values of a select box and display the same Form again. I know that I can change the values with $page->setConstants and I know that I can use Element->loadArray() to load the new values. But it seems that this only has an effect while the Form is not built or do I have some other mistake here? A second problem: How can I get Elements that are in a group with get Element? What is the name of these Elements? Even I set $appendName to false I cannot access the Element with it's name. Thanks Daniel