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
createRepository(repoName, "mock");
        createIndexWithContent("index-test");
        final List<String> snapshotNames = createNSnapshots(repoName, randomIntBetween(2, 5));
        final ActionFuture<CreateSnapshotResponse> snapshotThree = startAndBlockFailingFullSnapshot(repoName, "snap-other");
        final String masterName = internalCluster().getMasterName();
        final String snapshotOne = snapshotNames.get(0);
        final ActionFuture<AcknowledgedResponse> deleteSnapshotOne = startDeleteSnapshot(repoName, snapshotOne);
        awaitNDeletionsInProgress(1);
        unblockNode(repoName, masterName);
        expectThrows(SnapshotException.class, snapshotThree::actionGet);
        assertAcked(deleteSnapshotOne.get());
    }
    public void testStartDeleteDuringFinalizationCleanup() throws Exception {
        final String masterName = internalCluster().startMasterOnlyNode();
        internalCluster().startDataOnlyNode();
        final String repoName = "test-repo";
        createRepository(repoName, "mock");
        createIndexWithContent("index-test");
        createNSnapshots(repoName, randomIntBetween(1, 5));
        final String snapshotName = "snap-name";
        blockMasterFromDeletingIndexNFile(repoName);
        final ActionFuture<CreateSnapshotResponse> snapshotFuture = startFullSnapshot(repoName, snapshotName);
        waitForBlock(masterName, repoName);
        final ActionFuture<AcknowledgedResponse> deleteFuture = startDeleteSnapshot(repoName, snapshotName);
        awaitNDeletionsInProgress(1);
        unblockNode(repoName, masterName);
        assertSuccessful(snapshotFuture);
        assertAcked(deleteFuture.get(30L, TimeUnit.SECONDS));
    }
    public void testEquivalentDeletesAreDeduplicated() throws Exception {