These prolly would not be strong enough?
Put tape around where you want to cut the wire (so it doesnt unwrap itself)
and use cut off wheel, Or a GOOD pair of large wire cutters
Thats for cutting tinker toys.....
here use this
Mechanics™ M563DB - Cut-Off Tool | O'Reilly Auto Parts
It would depend on what you are using for guy wire. Mack's suggestion of a hammer and sharp cold chisel is what most people use if the guy wire is the heavy 5/16 EHS stuff. It also works well on smaller cable like 1/8-1/4 stainless steel cable too.