loader should add before remove

We're looking to provide a seamless transition from "current summer student, future fall student" to "past summer student, current fall student" on the term changeover boundary. A simplified scenario is below, with (A), (B), and (C) standing in for Group UUIDs.

Before fall semester start, a student might be members of the following groups; (C) is a populated by the loader, looking for Current groups:

(A) Current Summer Students in L&S
(B) Future Fall Students in L&S
(C) All Current Students [via (A)]

To reduce processing churn, we pause processing in Grouper and run a script after midnight on the first day of fall semester to rename the groups, which results in these memberships for the user:

(A) Past Summer Students in L&S
(B) Current Fall Students in L&S
(C) All Current Students [via (A)]

When we turn the loader back on, because deletes happen first, (A) is removed from (C) before (B) is added, so the user loses all the memberships / eligibility granted to All Current Students. These m