Hi! I need help in Visual C++ programming

Im just curious, how program modify other program without recompiling it?

for example:some trojan like subseven and Bo2k have 3 diff program,
Server,client and the config program.

The config program modify the server's port,email-add and etc.. and save
changes to the server program.

can you make a very simple program that can do like that?not a trojan! but
a simple display message.

The server has a default msg of "this is the original message"

and when the config prog run. it prompt user for a text to type, so every time
server run, It will display what the user type!!

I hope you can help me !!!
Thank's in Advance!!!

You can mail me the source code at my e-mail add--> [email protected]

sorry on my english grammar!!! coz im from Philippines!!!