#!/bin/bash
s='/*some comment*/
void something_patternWord1()
{
   some_code;
   some_code;
   some_code_patternWord3;
   some_code;
}
/*some comment patternWord2'

sed --posix -e '/patternWord1/,/patternWord2/{/patternWord3/i\
   new_line_of_some_code;
}' <<< "$s"
echo "===================";
sed --posix -e '/patternWord1/,/patternWord2/{/patternWord3/i \ \ \ new_line_of_some_code;' -e '}' <<< "$s"