Affiliations for an event only

Open Events → Events → select your event → Edit Event → Details.

Create the affiliation among the school's available affiliations, then select it for the intended event. EventAffiliation links an event to a valid school affiliation. Giving forms have their own selected active affiliations; review those selections and leave the new affiliation unselected where it should not appear. Preserve affiliations required by tiered campaigns. Adding a school affiliation is not a reason to assume it must appear on every form.