It's a yes and no answer. You can enter each ticketed section "once only" with strictly no re-entry. Since your tickets will have a definite time-slot for entry into Nasrid Palace, make sure you make it there on time. You can leave the premises for a while after you finish Nasrid Palace and come back via Justice Gate to see the Generalife Gardens, Carlos V Palace and Alcazaba. However, for each of these you can enter only once and re-entry is not allowed. You can do Carlos V Museums whenever you wish and as often as you wish, as that is not ticketed.