I'm not sure what to call it, but "Switch-Back" seems to be a good term for when Ewan takes from both breasts, but still wants more, so I switch him back to the first breast to trigger another let-down.
Part of on-demand nursing is paying attention to the baby's feeding session to know if he or she seems satisfied, or wants to continue. I know that Ewan wants more milk if he is still sucking quickly and strongly.
Look for the suck-swallow-breathe, suck-swallow-breathe pattern to turn into suck-suck-suck-suck-suck-suck-suck-swallow-breathe. If he is sucking alot, but is not swallowing very much, I can tell that the milk let-down on that breast has tapered off, so I should switch him to the other one.
Occasionally, he will still be sucking strongly after taking the second breast, so the only thing to do is to switch him back to the first one.
If this happens to you, don't get too worked up and think that you don't have enough milk. It's fine. The first breast may take a minute to let down again, but it will. This is more likely to happen in the evening, because everyone has "morning abundance" and "evening waning" milk. Morning milk is lower in fat and calories but there's more of it. Evening milk is higher in fat and calories, but there's less of it.
If the baby is going through a growth spurt or is just extra hungry for whatever reason, don't be afraid to "switch-back".