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
}
            return false;
        }, 30L, TimeUnit.SECONDS);
        assertTrue("No repository is blocked waiting on a data node", blocked);
    }
    public void unblockNode(final String repository, final String node) {
        logger.info("--> unblocking [{}] on node [{}]", repository, node);
        AbstractSnapshotIntegTestCase.<MockRepository>getRepositoryOnNode(repository, node).unblock();
    }
    protected void createRepository(String repoName, String type, Settings.Builder settings, boolean verify) {
        createRepository(logger, repoName, type, settings, verify);
    }
    public static void createRepository(Logger logger, String repoName, String type, Settings.Builder settings, boolean verify) {
        logger.info("--> creating or updating repository [{}] [{}]", repoName, type);
        assertAcked(clusterAdmin().preparePutRepository(repoName).setVerify(verify).setType(type).setSettings(settings));
    }
    protected void createRepository(String repoName, String type, Settings.Builder settings) {
        createRepository(repoName, type, settings, true);
    }
    protected void createRepository(String repoName, String type, Path location) {
        createRepository(repoName, type, Settings.builder().put("location", location));
    }
    protected void createRepository(String repoName, String type) {
        createRepository(logger, repoName, type);
    }
    protected void createRepositoryNoVerify(String repoName, String type) {
        createRepository(repoName, type, randomRepositorySettings(), false);
    }
    public static void createRepository(Logger logger, String repoName, String type) {
        createRepository(logger, repoName, type, randomRepositorySettings(), true);