There is always a risk of ceramic cracking so I would be very weary of that. However, you can get ceramic drill bits which will reduce the chances of cracking - I used one in a Belfast style sink once when I had to create holes for taps as I was too scared to knock through with a screwdriver.
thanks! actually managed to get a look at the problem first-hand, and it's one of the non-glazed parts, looks to be a manufacturing tolerance mess up, but only by a millimeter at most.
Father-in-law has a multitude of grinding bits, so fingers crossed it'll be fine.
Is it safe to use a dremel/drill to enlarge the holes in a ceramic toilet bowl to mount it to its frame (metal/built into the wall)?
For some reason the holes on the loo on the wall side are fine, but coming out the other end are too small to get the screws on the frame through.