The MODIFY COMMAND command is not available in the run-time (compiled EXE). See Run-time command restrictions in the help file for more commands that are not available (like MODIFY FORM,...).

As an alternative to the internal editor, you could use an external editor (such as NotePad++ or SciTE Editor which are both Open Source). And then use the RUN /N command to execute the editor as follows:

lcProgram = "c:\program files\notepad++\notepad++.exe" + ' "' + lcFileName + '"'
RUN /N &lcProgram

Note that the double-quotes above are to enclose the file name to account for spaces in the path.