Insert a line at specific line number with sed or awk

sed -n '16224,16482p;16483q' filename > newfile

From the sed manual:

p - Print out the pattern space (to the standard output). This command is usually only used in conjunction with the -n command-line option.

n - If auto-print is not disabled, print the pattern space, then, regardless, replace the pattern space with the next line of input. If there is no more input then sed exits without processing any more commands.

q - Exit sed without processing any more commands or input. Note that the current pattern space is printed if auto-print is not disabled with the -n option.

and

Addresses in a sed script can be in any of the following forms:

number Specifying a line number will match only that line in the input.

An address range can be specified by specifying two addresses separated by a comma (,). An address range matches lines starting from where the first address matches, and continues until the second address matches (inclusively).

Warning: This does not consider newlines. For a more in-depth answer, see this SO-question instead. (Thanks, Ed Morton & Niklas Peter)

Note that escaping everything is a bad idea. Sed needs many characters to be escaped to get their special meaning. For example, if you escape a digit in the replacement string, it will turn in to a backreference.

As Ben Blank said, there are only three characters that need to be escaped in the replacement string (escapes themselves, forward slash for end of statement and & for replace all):

ESCAPED_REPLACE=$(printf '%s\n' "$REPLACE" | sed -e 's/[\/&]/\\&/g')
# Now you can use ESCAPED_REPLACE in the original sed statement
sed "s/KEYWORD/$ESCAPED_REPLACE/g"

If you ever need to escape the KEYWORD string, the following is the one you need:

sed -e 's/[]\/$*.^[]/\\&/g'

And can be used by:

KEYWORD="The Keyword You Need";
ESCAPED_KEYWORD=$(printf '%s\n' "$KEYWORD" | sed -e 's/[]\/$*.^[]/\\&/g');

# Now you can use it inside the original sed statement to replace text
sed "s/$ESCAPED_KEYWORD/$ESCAPED_REPLACE/g"

Remember, if you use a character other than / as delimiter, you need replace the slash in the expressions above wih the character you are using. See PeterJCLaw's comment for explanation.

Edited: Due to some corner cases previously not accounted for, the commands above have changed several times. Check the edit history for details.