'Group by' autohide fields

I have a grid application that hides fields of the ‘Group by’ to not be redundant and get more compact view, but I have two problems:
-I don’t know how to show this fields again. Is there any onGroupByNone event? I hide them in field_onGroupBy event, but onGroupByAll is not valid to show again.
-When I export the grid to XML or XLS (in PDF works fine) I can’t get the ‘Group by’ field ‘header’. Is there any way to show this group fields in the exported data?.
-How can I change the label of the ‘Group by’ shown? Now shows the name of the grouped field, but I want to show the name of two fields that are common when they are grouped and not shown (I’ve hide them) to get compact view.

Thanks in advance.