change/edit exe on the fly

Hi:-


Case 1:

I want to edit exe on the fiy.

Before user downloads a exe, i have to add a "KEY" value in the exe so that when user installs the exe,

that "KEY" value is entered in the registry.

For example,

x.exe is a file.

I will reserve 4 bytes in the exe.

When user clicks on exe to download, i will assign some random number in the 4 bytes of exe as KEY value.

Then user will download that file.

Any one have idea how to do this?

By chaning the exe 4 bytes, the exe can not be invalid. The checksum to be computed again to validate

that exe.


Case 2:
 instead of reserving the 4 bytes, a txt file is already added in the exe with blank data. I will assign
the user KEY value in the txt file.  Now i need not build the exe again. Then user will download the
exe.


NOTE:

1. Current installer for the exe is GHOST installer

2. Exe was built on Windows98 and editing will happen on Linux machine in both cases( it is the JSP
server which starts Download process of user )

Over all, any other solution to the problem:

Change the exe on the fly to add a KEY value for the user before download starts

Advanced thanks