I was told by my dietician who, usefully, used to work in a diabetes specialist department, to half my insulin for the pre op diet. I did that and checked regularly as I did go very low (3.5) a couple of times so had to reduce further.
Following your op you will prolly not be needing insulin. If you do it will be very small doses.
Just make sure you test about four times a day so you can keep an eye on trends.