Add a script to arbitrarily change channels on image

scripts/image_signing/set_channel.sh

Index: scripts/image_signing/set_channel.sh
diff --git a/scripts/image_signing/set_channel.sh b/scripts/image_signing/set_channel.sh
new file mode 100755
index 0000000000000000000000000000000000000000..064d737f1ea8a4b4f393c051086b8a4032ff3520
--- /dev/null
+++ b/scripts/image_signing/set_channel.sh
@@ -0,0 +1,40 @@
+#!/bin/bash
+
+# Copyright (c) 2011 The Chromium OS Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+# Changes the channel on a Chrome OS image.
+
+# Load common constants and variables.
+. "$(dirname "$0")/common.sh"
+
+set -e
+
+if [ $# -ne 2 ]; then
+  cat <<EOF
+Usage: $PROG <image.bin> <channel>
+
+<image.bin>: Path to image.
+<channel>: The new channel of the image.
+EOF
+  exit 1
+fi
+
+main() {
+  local image=$1
+  local to=$2
+  
+  rootfs=$(make_temp_dir)
+  mount_image_partition "${image}" 3 "${rootfs}"
+  # Get the current channel on the image.
+  local from=$(grep '^CHROMEOS_RELEASE_TRACK=' \
+    "${rootfs}/etc/lsb-release" | cut -d '=' -f 2)
+  from=${from%"-channel"}
+  echo "Current channel is '${from}'. Changing to '${to}'."
+  sed -i "s/\b${from}\b/${to}/" "${rootfs}/etc/lsb-release" &&
+    echo "Channel change successful."
+  cat "${rootfs}/etc/lsb-release"
+}
+
+main "$@"