Thank you Klas.
I had to go to another way, since I have fields that are required to registered users and not required to guest users at the same time. I will let my solution using
seblod code pack if someone else need it too:
1) Add a javascript field to your form with this code to remove the class "required":
jQuery(function($){
$( "#my_field_id" ).removeClass( "validate[require[required_my_field_name]]" )
});<br>
2) Add a BeforeRender field to your form with this code to remove the "*" from the label of required field:
$fields['my_field_name']->required="";<br>
Of course you can put a conditional based in another field value in both steps to decide when the required class should be removed.
Hope It helps someone!