I think fileread is not the best option in this case. If you want to read the entire file, either use importdata or dlmread. If you want to skip some columns (e.g. for memory issues), you can use textscan (skip columns with the %*... specifier).
If you want to replace a specific value, either read the data, replace by A(32,4)=42; and save again or (a bit more tricky to realize) open the file, move to the position where you want to change something (fseek), write the new data and close the file. But then you need to know exactly the position in the file.
Best regards,
Michael