diff --git a/runtime/sync.sh b/runtime/sync.sh
index f30b410..a92a37e 100644
--- a/runtime/sync.sh
+++ b/runtime/sync.sh
@@ -3,9 +3,22 @@ set -Eeuo pipefail
 
 CONFIG_FILE="${PIWIGO_CONFIG:-/etc/bratonien-tools/nc-connector/connection-1.conf}"
 [[ -r "$CONFIG_FILE" ]] || { echo "Konfiguration fehlt: $CONFIG_FILE" >&2; exit 1; }
+
+# Preserve an explicit per-run override before the connection config is sourced.
+# This allows controlled shadow-tree updates without running the productive
+# Piwigo database synchronization, while leaving the stored config untouched.
+PIWIGO_SYNC_OVERRIDE_VALUE="${PIWIGO_SYNC_OVERRIDE-}"
+
 # shellcheck source=/dev/null
 source "$CONFIG_FILE"
 
+if [[ -n "$PIWIGO_SYNC_OVERRIDE_VALUE" ]]; then
+    case "$PIWIGO_SYNC_OVERRIDE_VALUE" in
+        0|1) PIWIGO_SYNC_ENABLED="$PIWIGO_SYNC_OVERRIDE_VALUE" ;;
+        *) echo "PIWIGO_SYNC_OVERRIDE muss 0 oder 1 sein." >&2; exit 1 ;;
+    esac
+fi
+
 install -d -m 0750 "$STATE_DIR"
 MANIFEST="$STATE_DIR/manifest.tsv"
 MAP_FILE="$STATE_DIR/name-map.json"