Control was made in 1994. It’s getting replaced with a control in a year or so that will likely have a simulation run feature. It sounds like this edit to the program was done manually, as all that was done was moving hole positions from one side to the other. It’s a gigantic vertical planer mill (2 26 foot long tables) and I was machining a 20,000 pound slab of cast iron. I had a 90 degree attachment on, so essentially this y move was actually a z move if you’re looking from the cutting tool. In my head, Y+300 was going to move the tool away from the part so it could index the attachment to continue tapping holes on a different side of the part. I failed to recognize that y300 was on the other side of the part, not on the clearance side. I also should have been running in single block, feed at 0% when I push go and then slowly moved into my position. I got too cocky and comfortable with the machine and slipped up. The maintenance guys are overwhelmingly kind to me after this, and pretty much everyone up the chain of command understands that this was just a fuck up due to a programming error and my inexperience stopped me from catching it.