I'm assuming MSER is morphine sulfate extended release? I'm also assuming you mean 60mg a day, therefor you take 2 30mg pills per day?
If so, and if you are prescribed 60mg then it absolutely won't harm you to take a quarter of a pill. I'm not telling you take more but you may not be very impressed with the results of taking a quarter of a pill.
Prescribed 60mg MSER, having decent pain. Can I quarter a 30mg pill and take a piece (quarter) without harm? Would it even help?