Today if we detect concurrent modification of a snapshot repository then we mark it with `CORRUPTED_REPO_GEN` which blocks further writes to try and prevent additional damage to its contents. You can remove the marker by calling the register-repository API again, but this API will discard no-op re-registrations without taking any action. You can work around this by unregistering the repository first (which may be impossible if it's still in use for searchable snapshots) or by re-registering it with some trivial setting change (which seems hacky).

We should not consider it a no-op re-registration if the repository is currently marked with `CORRUPTED_REPO_GEN`, because doing this re-registration will re-read the repo contents and clear the corruption marker and therefore is not a no-op.
server/src/internalClusterTest/java/org/elasticsearch/snapshots/ConcurrentSnapshotsIT.java
assertAcked(deleteFuture.actionGet());
            } catch (RepositoryException rex) {
                
                assertThat(rex.repository(), is("_all"));
                assertThat(rex.getMessage(), endsWith("Failed to update cluster state during repository operation"));
            } catch (SnapshotMissingException sme) {
                
                
                
                assertThat(sme.getSnapshotName(), is(firstSnapshot));
            }
        }
        expectThrows(SnapshotException.class, snapshotThreeFuture::actionGet);
        logger.info("--> verify that all snapshots are gone and no more work is left in the cluster state");
        awaitNoMoreRunningOperations();
        assertThat(client().admin().cluster().prepareGetSnapshots(repoName).get().getSnapshots(), empty());
    }
    public void testAssertMultipleSnapshotsAndPrimaryFailOver() throws Exception {
        internalCluster().startMasterOnlyNode();
        final String dataNode = internalCluster().startDataOnlyNode();
        final String repoName = "test-repo";
        createRepository(repoName, "mock");
        final String testIndex = "index-one";
        createIndex(testIndex, Settings.builder().put(SETTING_NUMBER_OF_SHARDS, 1).put(SETTING_NUMBER_OF_REPLICAS, 1).build());
        ensureYellow(testIndex);
        indexDoc(testIndex, "some_id", "foo", "bar");
        blockDataNode(repoName, dataNode);
        final ActionFuture<CreateSnapshotResponse> firstSnapshotResponse = startFullSnapshotFromMasterClient(repoName, "snapshot-one");
        waitForBlock(dataNode, repoName);
        internalCluster().startDataOnlyNode();