Users can use the affects form on the bug page to change which project or distribution the bug affects. You can also select the affected package. Lp API users can assign a project, distribution, or package to the BugTask target property to change the affected bug target. The behaviour is similar to the way questions can be retargeted between projects and distributions. Affected series cannot be changed, though the affected series package can be.
Previously, users had to mark a bug affecting a project or distribution as invalid, then add a new affected project or distribution. This cluttered the UI, caused excessive emails, and made pages slower.