Overwriting Field-Values (not read-only)

Hi, thank you for the nice module.
I am trying to use your Module not for validation, but for auto correction.
E.g:
if ( $node->field_ort[0]['value'] ){
$node->field_ort[0]['value'] = ucwords(strtolower( $node->field_ort[0]['value'] ));
}

As you mentioned - the $node->field values are read only. So this doesnt work so far.
Is there a possibility to make the node values writeable so that the example above would work?

Thank you very much.