Quick bash script to create self-extracting .sh files /w Base64 encoded contents (e.g. binary, zip, etc)

create_self_extracting_script.sh

#!/bin/bash
#
# create_self_extracting_script.sh <INPUT_FILE> [<OUTPUT_SCRIPT>]
#
# Creates a self-extracting shell script containing INPUT_FILE as Base64-encoded
# bytes. When executed, the script writes INPUT_FILE and restores its permissions.
#
# (c) Jeff Ward, 2017
# MIT License

FILENAME=$1
SCRIPT=${2:-extract.sh}

if [[ $# -eq 0 ]] ; then
    echo "Usage: $0 INPUT_FILE [OUTPUT_SCRIPT]"
    exit 0
fi

if [ ! -f "$FILENAME" ]; then
    echo "File not found: $FILENAME"
    exit 1
fi

echo "Writing $SCRIPT"

# Capture current permissions
PERMS="644"
if [[ "$OSTYPE" == "linux-gnu" ]]; then
    PERMS=`stat -c "%a" "$FILENAME"`
elif [[ "$OSTYPE" == "darwin"* ]]; then
    PERMS=`stat -f "%A" "$FILENAME"`
fi

cat > "$SCRIPT" << EOF

FILENAME="$FILENAME"

# Extract the .zip file
LINES=\`awk '/^__BASE64_ARCHIVE__/ {print NR + 1; exit 0; }' "\$0"\`
tail -n+\$LINES "\$0" | base64 --decode > "\$FILENAME" || { echo "Failed to write \$FILENAME" ; exit 1; }

# Restore permissions
chmod $PERMS "\$FILENAME"

echo "Extracted ./\$FILENAME"
exit 0

__BASE64_ARCHIVE__
EOF

base64 "$FILENAME" >> "$SCRIPT"
chmod a+x "$SCRIPT"

Does this also give the possibility to extract the zip and rebuild the installer manually? Im wondering how the data can be extracted and you can modify the installer without having the original files present.