diff --git a/README.md b/README.md
index f16762b..e7d18a9 100644
--- a/README.md
+++ b/README.md
@@ -34,6 +34,27 @@ Send the players `https://<your-host>/setup-windows-packwiz.html` or
 `setup-linux-packwiz.html`. Those are generated with your real pack URL and
 server address already filled in.
 
+## Re-running
+
+`deploy.sh` is safe to run repeatedly, and re-running is the intended way to
+apply changed settings — a port change, a different heap size, or a run that
+failed partway and left things half-applied.
+
+Each run:
+
+1. Snapshots the dataset (`<pool>@predeploy-<timestamp>`)
+2. Stops the server if it was running
+3. Rewrites `server.properties`, `user_jvm_args.txt` and both unit files
+4. Moves any existing pack to `<pack>.bak.<timestamp>` and rebuilds it
+5. Regenerates the player guides
+6. Starts the server again if it had been running
+
+**The world and `/minecraft/mods` are never touched.** The pack is moved aside
+rather than deleted, so hand-edited `.pw.toml` files and any git history in the
+pack directory survive.
+
+`--keep-pack` skips the pack rebuild; `--no-snapshot` skips step 1.
+
 ## What's in here
 
 | Script | Runs as | Does |
diff --git a/build.sh b/build.sh
index 31c778b..87d2a88 100755
--- a/build.sh
+++ b/build.sh
@@ -29,7 +29,7 @@ FILES=(
 
 die()  { echo "error: $*" >&2; exit 1; }
 info() { echo ">>> $*"; }
-usage() { sed -n '2,11p' "$0" | sed 's/^# \?//'; exit "${1:-0}"; }
+usage() { awk 'NR>1 && /^#/ {sub(/^# ?/,""); print; next} NR>1 {exit}' "$0"; exit "${1:-0}"; }
 
 while [ $# -gt 0 ]; do
     case "$1" in
diff --git a/deploy.sh b/deploy.sh
index 3d3f04e..38a0f1c 100755
--- a/deploy.sh
+++ b/deploy.sh
@@ -9,17 +9,25 @@
 #   1. mc-service-setup.sh   (root)  — minecraft user, NeoForge, systemd units
 #   2. packwiz-setup.sh      (you)   — pack, mod index from the mirror, guides
 #
+# Safe to re-run. Each run snapshots the dataset, stops the server if it was
+# running, rebuilds config and the pack from scratch, and starts it back up.
+# The world and $SHARE/mods are never touched; an existing pack is moved aside
+# to <pack>.bak.<timestamp> rather than deleted.
+#
+#   --keep-pack     keep the existing pack instead of rebuilding it
+#   --no-snapshot   skip the pre-deploy ZFS snapshot
+#
 # Run as your normal user; it calls sudo for the parts that need it.
 
 set -euo pipefail
 
 NAME=""; AUTHOR=""; BASEURL=""; NFVER="latest"; MCVER="1.21.1"
-SHARE="/minecraft"; XMX="10G"; XMS="10G"; ACCEPT_EULA=""; PORT="25565"
+SHARE="/minecraft"; XMX="10G"; XMS="10G"; ACCEPT_EULA=""; PORT="25565"; KEEP_PACK=0; SNAPSHOT=1
 HERE="$(cd -- "$(dirname -- "${BASH_SOURCE[0]}")" && pwd)"
 
 die()  { echo "error: $*" >&2; exit 1; }
 step() { printf '\n\033[1m=== %s ===\033[0m\n\n' "$*"; }
-usage() { sed -n '2,13p' "$0" | sed 's/^# \?//'; exit "${1:-0}"; }
+usage() { awk 'NR>1 && /^#/ {sub(/^# ?/,""); print; next} NR>1 {exit}' "$0"; exit "${1:-0}"; }
 
 while [ $# -gt 0 ]; do
     case "$1" in
@@ -33,6 +41,8 @@ while [ $# -gt 0 ]; do
         -X|--xmx)       XMX="${2:-}"; shift 2 ;;
         -x|--xms)       XMS="${2:-}"; shift 2 ;;
         --accept-eula)  ACCEPT_EULA="--accept-eula"; shift ;;
+        --keep-pack)    KEEP_PACK=1; shift ;;
+        --no-snapshot)  SNAPSHOT=0; shift ;;
         -h|--help)      usage 0 ;;
         *) echo "unknown option: $1" >&2; usage 1 ;;
     esac
@@ -50,20 +60,57 @@ done
 # Fail early rather than halfway through, since step 1 makes system changes.
 sudo -v || die "sudo is required"
 
+# ------------------------------------------------------------ re-run prep ---
+
+# Re-running is expected: a run that failed partway leaves a half-applied state,
+# and later runs change settings that only take effect on a fresh start. So take
+# a snapshot, stop the server, redeploy, and put it back how it was.
+#
+# World data and $SHARE/mods are never touched by any of this.
+
+WAS_ACTIVE=0
+if systemctl is-active --quiet minecraft.service 2>/dev/null; then
+    WAS_ACTIVE=1
+fi
+
+if (( SNAPSHOT )) && mountpoint -q "$SHARE" && command -v zfs >/dev/null; then
+    DATASET="$(findmnt -no SOURCE "$SHARE" 2>/dev/null || true)"
+    if [ -n "$DATASET" ] && [ "$(findmnt -no FSTYPE "$SHARE")" = zfs ]; then
+        SNAP="$DATASET@predeploy-$(date +%Y%m%d%H%M%S)"
+        step "Snapshotting $SNAP"
+        sudo zfs snapshot "$SNAP" \
+            && echo "roll back with: sudo zfs rollback $SNAP" \
+            || die "zfs snapshot failed — pass --no-snapshot to deploy anyway"
+    fi
+fi
+
+if (( WAS_ACTIVE )); then
+    step "Stopping minecraft.service for redeploy"
+    sudo systemctl stop minecraft.service
+fi
+
 step "1/2  Minecraft systemd service"
 sudo "$HERE/mc-service-setup.sh" \
     -s "$SHARE" -A "$USER" -X "$XMX" -x "$XMS" -m "$MCVER" -p "$PORT" \
     ${NFVER:+-N "$NFVER"} ${ACCEPT_EULA}
 
+PACK_FORCE=""
+(( KEEP_PACK )) || PACK_FORCE="--force"
+
 step "2/2  packwiz pack and player guides"
 # The admin group membership from step 1 isn't active in this shell yet, so run
 # the pack setup under the new group explicitly rather than telling you to log
 # out and back in.
 if id -nG "$USER" | tr ' ' '\n' | grep -qx minecraft; then
-    "$HERE/packwiz-setup.sh" -n "$NAME" -a "$AUTHOR" -m "$MCVER" -u "$BASEURL" -s "$SHARE" -p "$PORT"
+    "$HERE/packwiz-setup.sh" -n "$NAME" -a "$AUTHOR" -m "$MCVER" -u "$BASEURL" -s "$SHARE" -p "$PORT" ${PACK_FORCE}
 else
     sg minecraft -c "$(printf '%q ' "$HERE/packwiz-setup.sh" -n "$NAME" -a "$AUTHOR" \
-        -m "$MCVER" -u "$BASEURL" -s "$SHARE" -p "$PORT")"
+        -m "$MCVER" -u "$BASEURL" -s "$SHARE" -p "$PORT" ${PACK_FORCE})"
+fi
+
+if (( WAS_ACTIVE )); then
+    step "Restarting minecraft.service"
+    sudo systemctl start minecraft.service
 fi
 
 step "Done"
diff --git a/mc-service-setup.sh b/mc-service-setup.sh
index 955153e..dbe6acd 100755
--- a/mc-service-setup.sh
+++ b/mc-service-setup.sh
@@ -31,7 +31,7 @@ FIFO="/run/minecraft-console"
 die()  { echo "error: $*" >&2; exit 1; }
 info() { echo ">>> $*"; }
 warn() { echo "    warning: $*" >&2; }
-usage() { sed -n '2,17p' "$0" | sed 's/^# \?//'; exit "${1:-0}"; }
+usage() { awk 'NR>1 && /^#/ {sub(/^# ?/,""); print; next} NR>1 {exit}' "$0"; exit "${1:-0}"; }
 
 while [ $# -gt 0 ]; do
     case "$1" in
diff --git a/packwiz-setup.sh b/packwiz-setup.sh
index b28b6af..c87b12b 100755
--- a/packwiz-setup.sh
+++ b/packwiz-setup.sh
@@ -30,11 +30,12 @@ PACK_URL=""               # defaults to $SITE_URL/packs/<slug>
 SERVER_ADDR=""            # defaults to the hostname of $SITE_URL
 MCPORT="25565"            # Minecraft port, shown in the guides
 GUIDES=1                  # write the player setup guides
+FORCE=0                   # move an existing pack aside and rebuild it
 
 die()  { echo "error: $*" >&2; exit 1; }
 info() { echo ">>> $*"; }
 warn() { echo "    warning: $*" >&2; }
-usage() { sed -n '2,15p' "$0" | sed 's/^# \?//'; exit "${1:-0}"; }
+usage() { awk 'NR>1 && /^#/ {sub(/^# ?/,""); print; next} NR>1 {exit}' "$0"; exit "${1:-0}"; }
 
 while [ $# -gt 0 ]; do
     case "$1" in
@@ -54,6 +55,7 @@ while [ $# -gt 0 ]; do
         -A|--server)    SERVER_ADDR="${2:-}"; shift 2 ;;
         -p|--port)      MCPORT="${2:-}"; shift 2 ;;
         --no-guides)    GUIDES=0; shift ;;
+        --force)        FORCE=1; shift ;;
         -h|--help)      usage 0 ;;
         *) echo "unknown option: $1" >&2; usage 1 ;;
     esac
@@ -165,8 +167,18 @@ fi
 
 # ------------------------------------------------------------------ init ----
 
-[ -e "$DIR/pack.toml" ] && die "$DIR/pack.toml already exists — refusing to overwrite
-     (run 'packwiz init --reinit' there if that's what you want)"
+if [ -e "$DIR/pack.toml" ]; then
+    if (( FORCE )); then
+        # Moved aside rather than deleted: the pack dir may hold hand-edited
+        # .pw.toml files or a git history, and a rebuild is not worth losing them.
+        bak="$DIR.bak.$(date +%Y%m%d%H%M%S)"
+        info "existing pack found — moving it to $bak"
+        mv "$DIR" "$bak"
+    else
+        die "$DIR/pack.toml already exists — refusing to overwrite
+     Pass --force to move it aside and rebuild, or 'packwiz init --reinit' there."
+    fi
+fi
 
 mkdir -p "$DIR"
 cd "$DIR"