I would like to help you out with your setup. You should first revert you files back to the original ones for PowerStore to get things working again.
Once you have things back to normal you can begin the updating. If you would like to add an additional field to the products you will first need to add this column to your db. Once you have done that you can update the product insert and update pages to include a form element for the new value. The next thing to do would be to update the DataAssist Insert and Update server behaviors so that the new value will be recorded in the db.
All of this should be worked out and tested before you do anything to the files on the front end of the store. Depending on what you would like to do on the front end of the store it might require some custom coding to get things worked out. Please post back with any questions or issues that you are experiencing in regards to the updates on the back end and we will help with what we can.