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.
test/framework/src/main/java/org/elasticsearch/snapshots/AbstractSnapshotIntegTestCase.java
}
    public static SnapshotInfo createFullSnapshot(Logger logger, String repoName, String snapshotName) {
        logger.info("--> creating full snapshot [{}] in [{}]", snapshotName, repoName);
        CreateSnapshotResponse createSnapshotResponse = clusterAdmin().prepareCreateSnapshot(repoName, snapshotName)
            .setIncludeGlobalState(true)
            .setWaitForCompletion(true)
            .get();
        final SnapshotInfo snapshotInfo = createSnapshotResponse.getSnapshotInfo();
        assertThat(snapshotInfo.successfulShards(), is(snapshotInfo.totalShards()));
        assertThat(snapshotInfo.state(), is(SnapshotState.SUCCESS));
        return snapshotInfo;
    }
    protected SnapshotInfo createSnapshot(String repositoryName, String snapshot, List<String> indices, List<String> featureStates) {
        logger.info("--> creating snapshot [{}] of {} in [{}]", snapshot, indices, repositoryName);
        final CreateSnapshotResponse response = client().admin()
            .cluster()
            .prepareCreateSnapshot(repositoryName, snapshot)
            .setIndices(indices.toArray(Strings.EMPTY_ARRAY))
            .setWaitForCompletion(true)
            .setFeatureStates(featureStates.toArray(Strings.EMPTY_ARRAY))
            .get();
        final SnapshotInfo snapshotInfo = response.getSnapshotInfo();
        assertThat(snapshotInfo.state(), is(SnapshotState.SUCCESS));
        assertThat(snapshotInfo.successfulShards(), equalTo(snapshotInfo.totalShards()));
        assertThat(snapshotInfo.failedShards(), equalTo(0));
        return snapshotInfo;
    }
    protected SnapshotInfo createSnapshot(String repositoryName, String snapshot, List<String> indices) {
        return createSnapshot(repositoryName, snapshot, indices, Collections.singletonList(NO_FEATURE_STATES_VALUE));
    }