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
if (randomBoolean()) {
            return null;
        }
        Map<String, Object> metadata = new HashMap<>();
        long fields = randomLongBetween(0, 4);
        for (int i = 0; i < fields; i++) {
            if (randomBoolean()) {
                metadata.put(
                    randomValueOtherThanMany(metadata::containsKey, () -> randomAlphaOfLengthBetween(2, 10)),
                    randomAlphaOfLengthBetween(5, 5)
                );
            } else {
                Map<String, Object> nested = new HashMap<>();
                long nestedFields = randomLongBetween(0, 4);
                for (int j = 0; j < nestedFields; j++) {
                    nested.put(
                        randomValueOtherThanMany(nested::containsKey, () -> randomAlphaOfLengthBetween(2, 10)),
                        randomAlphaOfLengthBetween(5, 5)
                    );
                }
                metadata.put(randomValueOtherThanMany(metadata::containsKey, () -> randomAlphaOfLengthBetween(2, 10)), nested);
            }
        }
        return metadata;
    }
    public static String[] matchAllPattern() {
        return randomBoolean() ? new String[] { "*" } : new String[] { TransportGetRepositoriesAction.ALL_PATTERN };
    }
}