iirc you should be able to keep your origional prom chip when flashing. I bought blank chips to program my PCM and kept the origional one. sadly Moates went out of business selling chips and the programmers and I have no clue where to get blank chips now. I had bought the programmer and a couple of chips for mine to toy with. the issue for us doing the flashing on our own is finding the definition files for that specific prom ID so we can change the tune in TunerPro. I can look at the code in the prom programming and see what definition file is needed but it's finding it that is the pain. I have a contact who I can't recall his name who sent me free of charge GM's last update for my truck which I used to tune off from but I got lucky finding the definition file online in the depths of the internet.
I can look for his contact if you want and post it. he's well known in the tuning communities and has a business doing this.
edit: I found his info. Lyndon Wester. I have his email and his website is linked below