It appears you just change it as you mentioned. (in E10 at least)
// Ice.Core.Session
public string PlantID
{
get
{
return this.plantID;
}
set
{
if (string.Equals(value, this.plantID, StringComparison.OrdinalIgnoreCase))
{
return;
}
this.sessionMod.SetPlant(value, out this.plantName);
this.plantID = value;
this.OnSessionChanged(Session.SessionChangedItem.Plant);
}