How to insert a line using sed before a pattern and after a line number?

You can either write a sed script file and use:

sed -f sed.script file1 ...

Or you can use (multiple) -e 'command' options:

sed -e '/SysAdmin/i\
Linux Scripting' -e '1,$s/A/a/' file1 ...

If you want to append something after a line, then:

sed -e '234a\
Text to insert after line 234' file1 ...