Overwrite single line of file

[chrispoliquin at gmail.com]

Hi,

I have about 900 text files (about 2 GB of data) and I need to make
some very specific changes to the last line of each file.  I'm
wondering if there is a way to just overwrite the last line of a file
or replace the spots I want (I even know the position of the
characters I need to replace).

I know how to open files and read the contents and then write
everything out again after making the changes, but is there a way to
replace just the last line without having to completely rewrite each
file after making the changes?

-Chris