@@ -38,6 +38,38 @@ def test_apply_diff_to_model_applies_plain_field(db):
     assert presentation.slideshow_url == "https://example.com/new"
 
 
+def test_apply_diff_to_model_ignores_reordered_reverse_relation(db):
+    presentation = baker.make(Presentation)
+    speakers = baker.make(PresentationSpeaker, presentation=presentation, _quantity=2)
+    diff = {model_to_identifier(presentation): {"speakers": [model_to_identifier(s) for s in reversed(speakers)]}}
+
+    apply_diff_to_model(diff)
+
+    assert set(presentation.speakers.values_list("id", flat=True)) == {s.pk for s in speakers}
+
+
+def test_apply_diff_to_model_rejects_member_change_on_non_nullable_reverse_relation(db):
+    presentation = baker.make(Presentation)
+    speakers = baker.make(PresentationSpeaker, presentation=presentation, _quantity=2)
+    diff = {model_to_identifier(presentation): {"speakers": [model_to_identifier(speakers[0])]}}
+
+    with pytest.raises(ValueError, match="speakers"):
+        apply_diff_to_model(diff)
+
+    assert presentation.speakers.count() == 2
+
+
+def test_apply_diff_to_model_applies_many_to_many_members(db):
+    presentation = baker.make(Presentation)
+    old_category, new_category = baker.make(PresentationCategory, type=presentation.type, _quantity=2)
+    baker.make(PresentationCategoryRelation, presentation=presentation, category=old_category)
+    diff = {model_to_identifier(presentation): {"categories": [model_to_identifier(new_category)]}}
+
+    apply_diff_to_model(diff)
+
+    assert set(presentation.categories.values_list("id", flat=True)) == {new_category.pk}
+
+
 def test_model_to_jsonable_dict_sorts_reverse_relation_identifiers(db):
     presentation = baker.make(Presentation)
     speakers = baker.make(PresentationSpeaker, presentation=presentation, _quantity=3)
 
@@ -262,6 +262,21 @@ def json_to_simplenamespace(model_data: dict[str, dict[str, typing.Any]], key: s
     return resolved_models[key]
 
 
+def _apply_related_diff(manager: models.manager.BaseManager, field_name: str, identifiers: list[str]) -> None:
+    related_model_instances = [identifier_to_model(item) for item in identifiers]
+    if None in related_model_instances:
+        raise ValueError(f"One or more related models not found for identifiers: {identifiers}")
+
+    if {item.pk for item in manager.all()} == {item.pk for item in related_model_instances}:
+        return
+
+    # 역참조 FK의 remove()는 Django가 field.null=True일 때만 제공하므로, 그 외에는 구성원 변경을 적용할 수 없다.
+    if not hasattr(manager, "remove"):
+        raise ValueError(f"Cannot change members of the non-nullable reverse relation '{field_name}'")
+
+    manager.set(related_model_instances)
+
+
 def apply_diff_to_model(models_data: dict[str, dict[str, typing.Any]]) -> list[models.Model]:
     result_instances: list[models.Model] = []
 
@@ -285,20 +300,11 @@ def apply_diff_to_model(models_data: dict[str, dict[str, typing.Any]]) -> list[m
                 if not (related_model_instance := identifier_to_model(value)):
                     raise ValueError(f"Related model not found for identifier: {value}")
                 setattr(model_instance, field_name, related_model_instance)
-            elif isinstance(value, collections.abc.Iterable) and value and all(is_identifier(item) for item in value):
-                # If the value is a list of model identifiers, resolve them to model instances
-                related_model_instances = [identifier_to_model(item) for item in value]
-                if None in related_model_instances:
-                    raise ValueError(f"One or more related models not found for identifiers: {value}")
-
-                old_related_models = {item.pk: item for item in getattr(model_instance, field_name, [])}
-                new_related_models = {item.pk: item for item in related_model_instances}
-
-                field = getattr(model_instance, field_name)
-                for del_pk in old_related_models.keys() - new_related_models.keys():
-                    field.remove(old_related_models[del_pk])
-                for add_pk in new_related_models.keys() - old_related_models.keys():
-                    field.add(new_related_models[add_pk])
+            elif is_identifier_list(value) and isinstance(
+                related_manager := getattr(model_instance, field_name, None), models.manager.BaseManager
+            ):
+                # If the value is a list of model identifiers, it is an m2m/reverse relation
+                _apply_related_diff(related_manager, field_name, value)
             else:
                 setattr(model_instance, field_name, value)
 
 
@@ -2,8 +2,12 @@
 from types import SimpleNamespace
 
 import pytest
+from core.util.django_orm import model_to_identifier
 from core.util.thread_local import thread_local
+from django.contrib.contenttypes.models import ContentType
 from django.utils.translation import override
+from event.presentation.models import Presentation, PresentationSpeaker
+from model_bakery import baker
 from participant_portal_api.models import ModificationAudit
 from participant_portal_api.serializers.user import UserPortalSerializer
 from rest_framework import status
@@ -75,3 +79,27 @@ def test_approve_ko_nickname_request_under_en_locale_keeps_en_nickname(requester
     requester.refresh_from_db()
     assert requester.nickname_ko == "새한글이름"
     assert requester.nickname_en == "EnglishName"
+
+
+def test_approve_presentation_audit_with_reordered_speakers(db, admin_client):
+    """발표자 순서만 뒤집힌 채 저장된 과거 수정 요청도 승인할 수 있어야 한다."""
+    presentation = baker.make(Presentation)
+    speakers = baker.make(PresentationSpeaker, presentation=presentation, biography_ko="이전 소개", _quantity=2)
+    audit = ModificationAudit.objects.create(
+        instance_type=ContentType.objects.get_for_model(Presentation),
+        instance_id=str(presentation.pk),
+        original_data={model_to_identifier(presentation): {}},
+        modification_data={
+            model_to_identifier(presentation): {
+                "speakers": [model_to_identifier(speaker) for speaker in reversed(speakers)]
+            },
+            model_to_identifier(speakers[0]): {"biography_ko": "새 소개"},
+        },
+    )
+
+    response = admin_client.patch(APPROVE_URL.format(audit_id=audit.id), data={}, format="json")
+
+    assert response.status_code == status.HTTP_200_OK, response.data
+    speakers[0].refresh_from_db()
+    assert speakers[0].biography_ko == "새 소개"
+    assert set(presentation.speakers.values_list("id", flat=True)) == {speaker.pk for speaker in speakers}