From what I could make out of your problem:
1.You have a program or an executable which creates a file
2.Every time you run the program the file created previously gets
"overwritten"
3.You want new file to get created every time you run the program in your cron.

The solution lies in changing the very program that creates the file.
If you have the code of that program then probably someone can help.

Chill
enc.