About linux : search-a-pattern-in-file-and-insertappend-a-string-in-specific-position

I am completely new to sed script. I have been researching how to add text to a file and managed to get the text I want adding to the correct line in the file but can not find a way to add it to the correct position!
so the line I have in the text file looks like this

/^From: \s*(.*@)?(((test\.new\.com)))/ REJECT You are not me

and i want to get input from user and add input to above line, which result should be like below, user input is “test2.newer.com” and i want to add this string |(test2\.newer\.com)

/^From: \s*(.*@)?(((test\.new\.com)|(test2.\newer\.com)))/ REJECT You are not me

i try this but not working

read -p "Enter new domain: " newdomain
file="./testfile"
sed -i "/You are not me/ s/^\(.*\)\())\)/\1, |($newdomain)\2/" $file

how do I go about adding it to the correct position?

With Escape a string for a sed replace pattern you can replace any line content that you want.

lineinfile='/^From: \s*(.*@)?(((test\.new\.com)))/ REJECT You are not me'
newcontent='/^From: \s*(.*@)?(((test\.new\.com)|(test2.\newer\.com)))/ REJECT You are not me'

ESCAPED_KEYWORD=$(printf '%s\n' "$lineinfile" | sed -e 's/[]\/$*.^[]/\\&/g');
ESCAPED_REPLACE=$(printf '%s\n' "$newlinecontent" | sed -e 's/[\/&]/\\&/g')
sed "s/$ESCAPED_KEYWORD/$ESCAPED_REPLACE/g"

Using sed

$ newdomain="(test2.\\\newer\.com)"
$ sed "s|\([^)]*.[^)]*)\)\(.*\)|\1\|$newdomain\2|" input_file
/^From: \s*(.*@)?(((test\.new\.com)|(test2.\newer.com)))/ REJECT You are not me

With
newdomain='test2\.newer\.com'
you can use the awk command

awk -v repl="${newdomain//\\/\\\\}" '
  BEGIN {OFS=FS=")))"}
  /You are not me/ {$1=$1 ")|(" repl}
  1
' "$file" > "$file".new && mv "$file".new "$file"

Explanation:
${newdomain//\\/\\\\}" awk wants to treat the escape sequence \. treated as a ., so add backslashes.
BEGIN {OFS=FS=")))"} Before parsing lines set “)))” as field separator (input and output).
/You are not me/ Change lines with this substring.
$1=$1 ")|(" repl' Append )|( and the string in repl to $1.
1 Print the line.
"$file" > "$file".new && mv "$file".new "$file" Dpn’t edit in place but redirect to a new file and move that file to the original file when awk succeeded.

thanks guys i find my problem and answer is like this:

read -p "Enter domain: " newdomain
sed -i "/You are not me/ s/\()))\)/)|$newdomain)))/' $file

but the output is like this:

/^From: \s*(.*@)?(((test\.new\.com)|(test2.newer.com)))/ REJECT You are not me

but i want this output:

/^From: \s*(.*@)?(((test\.new\.com)|(test2.\newer\.com)))/ REJECT You are not me