Please follow below steps to change the long name:
1. Copy the below script lines to a new C file in Code Builder, save and  Compile it:
void SetDatasetLongName(string dsName, string strLN)
{
	DatasetObject dsObj(dsName);
	if (dsObj)
		dsObj.SetLabel(strLN, RCLT_LONG_NAME, FALSE);
}
2. Go back to Origin workspace, in the Script Window or Command window, run the below script line to call the function defined above in Labtalk : 
SetDatasetLongName("F1", "somename");
Originlab Technical Service Team