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
.cluster()
            .prepareCreateSnapshot(repoName, "snapshot-three")
            .setIndices(secondIndex)
            .setWaitForCompletion(true)
            .execute();
        assertThat(firstSnapshotResponse.isDone(), is(false));
        assertThat(secondSnapshotResponse.isDone(), is(false));
        unblockNode(repoName, dataNode);
        final SnapshotInfo firstSnapshotInfo = firstSnapshotResponse.get().getSnapshotInfo();
        assertThat(firstSnapshotInfo.state(), is(SnapshotState.FAILED));
        assertThat(firstSnapshotInfo.reason(), is("Snapshot was aborted by deletion"));
        final SnapshotInfo secondSnapshotInfo = assertSuccessful(secondSnapshotResponse);
        final SnapshotInfo thirdSnapshotInfo = assertSuccessful(thirdSnapshotResponse);
        assertThat(deleteSnapshotsResponse.get().isAcknowledged(), is(true));
        logger.info("--> verify that the first snapshot is gone");
        assertThat(
            client().admin().cluster().prepareGetSnapshots(repoName).get().getSnapshots(),
            containsInAnyOrder(secondSnapshotInfo, thirdSnapshotInfo)
        );
    }
    public void testCascadedAborts() throws Exception {
        internalCluster().startMasterOnlyNode();
        final String dataNode = internalCluster().startDataOnlyNode();
        final String repoName = "test-repo";
        createRepository(repoName, "mock");
        createIndexWithContent("index-one");
        final String firstSnapshot = "snapshot-one";
        final ActionFuture<CreateSnapshotResponse> firstSnapshotResponse = startFullSnapshotBlockedOnDataNode(
            firstSnapshot,
            repoName,