Unfortunately MATLAB does not support the operating system operations needed to truncate a file. Would replacing the deleted section with blanks be acceptable?
The operating systems themselves do not support any operations to insert or delete text inside a file, or to modify text (exception: if the modification is exactly the same size as the original). The operating systems do support truncating files, but MATLAB does not make that available.
Thus if one wants to change a text file, the strategy is to open a new file, copy the original file over to the new file until one gets to the part that needs to be changed, write out the changed text, and then resume copying the input file to the output file. After everything is done, you may rename the output file to the name of the original file.
