Change values in an imported text file, for so exporting back to a new text file

I have an stl/text file where I would like to locate and change values. The file represents a geometry. After the file is altered I need to export is back in the same layout as it was imported. Any ideas?

[KSSV]

Can be done....you have to show the format of your file.

[Carl]

I second KSSV's comment. Since the issue includes reading from, altering, and preserving a specific layout of your file, it would be helpful if you could show the format.