Not sure I mentioned it elsewhere but I flipped the top of my Ikea Fredde desk around earlier in the year as I was tired of notch that is cut out of it. I had to re-drill some holes but it went back together perfectly and it's much better with a flat front, it meant that I could get a new desk mat too and didn't need to cut a chunk out of it.
Anyway the only issue was that the corner holes at the back were smaller than those at the front, so my pen holder didn't fit. It took a while to get to it as I was waiting for the 79mm Bosch holesaw to get cheaper but when I got it I 3D printed this template thingy and screwed it to a piece of plywood, I could clamp the plywood and there's now a hole to guide the centre drill of the holesaw.
It needed to be drilled to one side as it would otherwise be too close to the edge of the desk. There's a flat on the edge where the holesaw will be the closest so it doesn't cut into the template
It worked perfectly and I got this crescent of desk. I used my right angle Makita drill for this as it gave me the best chance of keeping it square.