var group = people.getGroup("GROUP_MYGROUP");
var nodes = people.getPeople("mypeople*");

logger.log("found:" + nodes.length); 
logger.log("\n");

for each(var node in nodes)
{
  user = utils.getNodeFromString(node); 
  people.addAuthority(group, user);
  //people.removeAuthority(group, user);
  
  logger.log(user.properties["cm:userName"]); 
  
}