Run custom PHP after file upload

[Flabaliki]

Hey, this may seem a bit confusing at first, but I'll try to explain it as best as I can.

I'll be using Xthreads to manage file uploads. One of the file types that I'll be allowing (.Sims3Pack) has a bunch of stuff in it that essentially doesn't need to be there. I am able to modify the file via PHP successfully and have done so in the past.

My question is this; do you have any idea how I could run this PHP code after the file has been uploaded so that I can update this file and remove the unnecessary content?

In short, I want to modify a file after it has been uploaded and save the new file over the uploaded one.

Thanks for any help!