Yes, you can cut it. A hacksaw will work, as will a reciprocating saw. I don’t have any flexible combo rods anyway. You can get some idea of how long the anode should be by measuring from the top down to the drain valve. The anode should extend almost to the bottom, and the drain valve marks that.
When I finally get some new flex anodes, you’ll no longer have to worry about snapping them. I’m going to the loose-link variety.