The e-Boarding Passes (if you mean Mr. Easy Checkin Online) have a barcode with all the pertinant info (name, PNR, seat assignments, etc). So even editing the text won't change the data on the barcode.

Also, if you present a BP with a seat not currently assigned as "filled" in the system, I expect the computer will flash an error. Then when the GA tries to identify you, they will see you have no reservation and then it truly will be fraud and your next flight will probably be on Con Air.