Apply one multi-select option delta — most often a tag — to many entities in a single call. Use this instead of calling SetEntityProperty once per entity when the user asks to tag or label a set of items at once (e.g. “tag the last 50 emails as Follow-up”). Provide the property_definition_id (a tag set’s propertyDefinitionId from ListTags) and the option ids to add and/or remove (a tag’s option id from ListTags). The same add_option_ids/remove_option_ids delta is applied to every entity, composing atomically with concurrent edits per entity. Only for multi-select or tag properties; for other value types, or a single entity, use SetEntityProperty. Up to 200 entities per call — split larger sets across multiple calls. Best-effort: each entity is handled independently. Entities you don’t have edit access to are reported with status ‘skipped_no_permission’ and left unchanged, entities that can’t take the property are ‘failed’, and the rest are ‘applied’ — one call never fails wholesale because a few entities were not editable. Inspect the per-entity results and the summary to see what happened.