Registration is open and you have discovered something is set up wrong. Most things can be caught up on, but almost nothing applies retroactively — new rules take effect from the moment you introduce them, and older data has to be evened out by hand. This overview says where to expect manual work and what can no longer be fixed at all.
Before you change anything, find out how many people it affects. With five registrations a manual fix is a matter of minutes; with five hundred it is the reason to pick a different approach.
Group assignment — groups can be assigned in bulk in Contacts and groups. Automatic assignment by a form answer, however, applies only to new answers; existing ones are not backfilled into the group.
A missing preferred language — fill it in on the contact or by import. It does not affect e-mails that already went out.
A new custom contact field — you can create the field any time, but it stays empty for earlier registrations. Fill it in manually or by import.
Billing details — a correction creates a new version of the invoice; the original stays in the order history.
Session capacity — you can raise it any time. Lowering it below the number already signed up does not cancel anyone's registration.
Attendee status — it can be switched by hand in the Registration section (to Not attending after a phone call, for example).
Sent e-mails. You cannot rewrite the text or a link in a message that has gone out. When the mistake matters, you can send a correction targeted at the affected group only.
A completed campaign mailing. Only a mailing that is still running can be deleted.
Optional consents for earlier registrations. A consent added later does not cover people who registered before it; you have to approach them separately.
The event's primary language. It cannot be changed once the event is created.
Missing data from automatic registration. Someone who never went through the form has no answers — the only route is to ask them afterwards.
For a campaign, copying usually beats fixing: Copy → edit → send to the right segment. For the event itself that rarely applies, because a copy carries neither registrations nor contacts.
Assigning a group in bulk is one action, but it only covers the people who are in the system at that moment. Anyone registering tomorrow will not land in the group unless you also set up automatic assignment. So after a manual fix, always add the forward-looking rule too.
Before a bulk action over hundreds of contacts, export the current state. When a bulk change lands somewhere other than you intended, that export is the only way back.
