clarify exporting data into existing indexes

Author: guimachiavelli

reference/api/export.mdx

@@ -15,6 +15,8 @@ Use the `/export` route to transfer data from your origin instance to a remote t
 
 Migrate data from the origin instance to a target instance.
 
+Migration is an additive operation. If the exported indexes already exist in the target instance, Meilisearch keeps the existing documents intact and adds the new data to the index.
+
 ### Body
 
 | Name                | Type   | Default value | Description                                                                                               |
@@ -32,7 +34,7 @@ This field is required.
 
 #### `apiKey`
 
-A security key with full admin permissions to a secured Meilisearch instance.
+A security key with `index.create`, `settings.update`, and `documents.add` permissions to a secured Meilisearch instance.
 
 #### `payloadSize`
 
@@ -42,10 +44,12 @@ The maximum size of each single data payload in a human-readable format such as
 
 A set of objects whose keys correspond to patterns matching the indexes you want to export. By default, Meilisearch exports all documents across all indexes.
 
+Meilisearch does not override any index settings by default. If the target instance contains an index with the same name as an index you're exporting, Meilisearch uses the settings in the target instance. If the index does not already exist in the target instance, Meilisearch uses the settings in the origin instance.
+
 Each index object accepts the following fields:
 
 - `filter`: a [filter expression](/learn/filtering_and_sorting/filter_expression_reference) defining the subset of documents to export. Optional, defaults to `null`
-- `overrideSettings`: if `false`, uses the index settings as configured in the origin instance. if `true`, uses the target instance settings. Optional, defaults to `false`.
+- `overrideSettings`: if `true`, configures indexes in the target instance with the origin instance settings. Optional, defaults to `false`
 
 ### Example