Deduplication happens once, when an alert is written, so a change to the shape algorithm only affects alerts raised after it. This applies the current algorithm to alerts already stored: faults the old rules split apart are folded together, and alerts the new rules consider different are separated again. Alerts somebody has acknowledged, assigned or closed keep their status and link - only their fingerprint is refreshed - so nothing disappears from an operator's queue. Defaults to a dry run; the response is identical either way, so rehearse first and read shapeChanged and shapesBefore/shapesAfter before writing.