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/main/java/org/elasticsearch/repositories/RepositoriesService.java
return;
        }
        submitUnbatchedTask(
            clusterService,
            "update repository UUID [" + repositoryName + "] to [" + repositoryUuid + "]",
            new ClusterStateUpdateTask() {
                @Override
                public ClusterState execute(ClusterState currentState) {
                    final RepositoriesMetadata currentReposMetadata = currentState.metadata()
                        .custom(RepositoriesMetadata.TYPE, RepositoriesMetadata.EMPTY);
                    final RepositoryMetadata repositoryMetadata = currentReposMetadata.repository(repositoryName);
                    if (repositoryMetadata == null || repositoryMetadata.uuid().equals(repositoryUuid)) {
                        return currentState;
                    } else {
                        final RepositoriesMetadata newReposMetadata = currentReposMetadata.withUuid(repositoryName, repositoryUuid);
                        final Metadata.Builder metadata = Metadata.builder(currentState.metadata())
                            .putCustom(RepositoriesMetadata.TYPE, newReposMetadata);
                        return ClusterState.builder(currentState).metadata(metadata).build();
                    }
                }
                @Override
                public void onFailure(Exception e) {
                    listener.onFailure(e);
                }
                @Override
                public void clusterStateProcessed(ClusterState oldState, ClusterState newState) {
                    listener.onResponse(null);
                }
            }
        );