FROM: http://www.msfn.org/board/Fedit_t48200.html

  -add
     Tells Fedit to add LINE.
  -rem
     Tells Fedit to remove LINE.
  -f "some file"
     The file to be edited
  -l "some text"
     The text to be added or removed

When adding, these are additional (optional) parameters:
  -a[:co] "some text"
     The text will be added after this line
  -b[:co] "some text"
     The text will be added before this line
  -s[:c] "some text"
     The text will be added in the section [some text]
  -once
     The text to be added, will only be added once in the whole file
  -create
     If the section isn't found, it will be created

When removing, -l supports the parameter [:co], and these additional
(optional) parameters:
  -a[:co] "some text"
     All instances of the text after this line will be removed.
  -b[:co] "some text"
     All instances of the text before this line will be removed.
  -s[:c] "some text"
     All instances of the text in section [some text] will be removed.
  -once
     The text to be removed, will only be removed once.

The option [:co] means the following:
If you have a parameter -a "some text", Fedit will automatically search for
strings that match it (without being case sensitive). If you want it to be
case sensitive, change it to this:
  -a:c "some text"
If you think that 'some text' is contained in a bigger string like 'this is
some text written somewhere', then change it to this:
  -a:o "some text"
You can combine both to this:
  -a:co "some text"

IMPORTANT: none of the parameters are case sensitive, so for example -rem is
  the same as -Rem or -REM. Same thing for -a:co or -A:CO
IMPORTANT: the order of the parameters is unimportant, so:
  Fedit -rem -f file -l:co text
Is the same as:
  Fedit -f file -l:oc text -rem