Interesting requirements, OOTB cannot achieve it, you need customization, refer to this code
API VersionControlHelper.setIterationIdentifier(Iterated iteration, IterationIdentifier identifier)
Demo
// iterate part from A.1 to A.5
WTPart newPart = (WTPart) VersionControlHelper.service.newIteration( part, true );
//Refresh the old iteration
part = (WTPart)PersistenceHelper.manager.refresh(part);
//Build the relationship between the new and old iteration
newPart =(WTPart)VersionControlHelper.service.supersede(part, newPart);
//Set the iterationIdentifier of new iterations
VersionControlHelper.setIterationIdentifier((Iterated)newPart,IterationIdentifier.newIterationIdentifier(Series.newSeries("wt.vc.IterationIdentifier", "5")));
//Store the new iteration
PersistenceHelper.manager.store(newPart);