How do I replace a single word in a text file while maintaining all other text?

I have a text file (Original_Text.txt) containing the following lines;

ESPN is on sale

Other text

ESPN can be found here

some more text

ESPN costs this much

Last of the text

I am attempting to replace ESPN with ESPN_Magazine while retain all other text in the file. The resulting Modified_Text.txt file should contain the following;

ESPN_Magazine is on sale

Other text

ESPN_Magazine can be found here

some more text

ESPN_Magazine costs this much

Last of the text

I am using the following MATLAB code;

% Clear variables, close all open files, and clear out the command window
clear all;
fclose('all');
clc;
% open files for reading and writing
Original_File = fopen('Original_Text.txt','r') ;
Modified_File = fopen('Modified_Text.txt','w') ;
% Replace all occurences of ESPN with ESPN_Magazine while retain all other
% text in the file
while ( ~feof(Original_File) )
  % read line from original text file
  str = fgets(Original_File) ;
  % match line to regular expression to determine if replacement needed
  match = regexp(str,'ESPN ', 'match') ;
  % if ESPN is to be replaced
  if ( ~isempty(match) ) 
    str = ['ESPN_Magazine ', char(10)] ;
  end
  % write line to modified text filewriting file
  fwrite(Modified_File,str) ;
end
fclose('all');

And I’m getting the following result:

ESPN_Magazine

Other text

ESPN_Magazine

some more text

ESPN_Magazine

Last of the text

How do I get MATLAB to include the rest of the text from the original file?