It's always possible. The question is how. There is a TecUtil function to create isozones from a zone, and setting the contour level to a specific number will create the iso-surface. So you use TecUtilContourLevelX to set up the contour level for an iso-surface, then the TecUtilCreateIsoZones command to extract the iso-surface to a zone. Once the iso-zone is established, you can use a variety of methods of selecting regions of elements to extract a region.
Aerospace Research Engineer
NASA Langley Research Center