China DOS Union

Like this.
Modify some text under DOS, for example:
find the [network] field and add something like domain=111 after that line.
Or replace "windows xp" with "xp"
Or delete only the line that contains the string “cpl.hlp”.
...
In the past I always used echo together with findstr, which was a real hassle, and echo is kind of lousy for that.

I wonder whether you experts can recommend a command-line tool for this, something invoked from the command line, not an editor.

Why does the term CPL sound so familiar?
CPL — circular polarizing lens, haha...

It seems there isn't any direct internal command with that kind of function :）

The built-in findstr in XP can delete lines containing a specific string.
The main problem is that the following functions don't work well when combined with echo.
I just want to achieve these few functions:
1. Delete a specific string without deleting the line containing that string.
2. Replace a specific string.
3. Insert a line after the line containing a specific string, and write specific content into it.

The text handled by echo is very irregular, and GNU sed is too hard to use.

Experts, please a