Hola Daniel,
If you really work with the XML file exported from the selections, they contain
the nodal/elemental IDs. Therefore, this will always select the same exported
selection. But if you export the selections as geometry, e.g. export heads at
the nodal selection as SHP file, then you can import the SHP in the Maps panel.
This process will allow to select at any target slice by using the tools Select
by Map Point/Line/Polygon.
Saludos
Carlos