I am using activiti 5.17.0. I would like to know whether it is possible to reassign task from user to group and vice versa at runtime?. I know that it is possible to assign task from one user to another.
Yes, you can reassign a task from a user to a group and vice versa. Depending on your requirements you might want to set the assignee to null when reassigning a task to a group (and setting the identity link type to candidate in case you want the task to be reclaimable by users).