Can a workflow robot assign a participant to a subsequent task?

try below code snippet, and make changes on according to your business. 

/**
* Below snippet will get the defined group
*/
String propertiesPath = "ext.test.workflowconfig";
String key = "China";
String groupName = "";
ResourceBundle resourceBundle = ResourceBundle.getBundle(propertiesPath);
if(resourceBundle.containsKey(key)) {
groupName = resourceBundle.getString(key);
}

/***
* Below snippet will get the group name
*/
WTGroup wtgroup = null;
QuerySpec querySpec = new QuerySpec(WTGroup.class);
querySpec.appendWhere(new SearchCondition(WTGroup.class, WTGroup.NAME, SearchCondition.EQUAL, groupName, false), new int[] {0});
for(QueryResult queryResult = PersistenceHelper.manager.find((StatementSpec)querySpec); queryResult != null && queryResult.hasMoreElements();)
wtgroup = (WTGroup)queryResult.nextElement();

/**
* Get users from the group and put into a ArrayList
*/
ArrayList<WTUser> members = new ArrayList<WTUser>();
Enumeration<?> member = wtgroup.members();
while (member.hasMoreElements()) {
WTPrincipal principal = (WTPrincipal) member.nextElement();
if (principal instanceof WTUser)
members.add((WTUser) principal);
}

/**
* Add users to roles in the team.
*/

TeamManaged teamManaged = null; // here you can cast your primaryBusinessOjbect into this teamManaged
TeamReference teamRef = teamManaged.getTeamId();
Team team = (Team)teamRef.getObject();
Role role = Role.toRole("roleName");
for(int i =0; i <members.size(); i ++) {
WTPrincipal wtprincial = members.get(i);
team.addPrincipal(role, wtprincial);
}
team = (Team)PersistenceHelper.manager.refresh(team);