For our 19H I had to cut after the first hole. Your 23B is a larger model, so you may not need to cut at all, test fit it first. Cut through the solid web between the holes, and if you do cut, cut them both down so your wheels will rise evenly.
I cut mine on a sliding compound mitre saw, using the wedge to hold it flat. It may be good to use a hand saw however - I created a major pink snowstorm in my driveway with power saw. The plastic itself cuts very easily so I think a hand saw might work. If you can, clamp it into a mitre jig to get a straight cut. If using a jig saw, I would clamp a straight edge across the leveller to guide the saw.
2011 Jayco X19H (purchased 2015)
2008 Jayco 1007 PUP (purchased new, traded for the X19)
2012 Chev Traverse LT with TP