I assume this is really fine brass mesh. First you need a really strong magnifier (I use Optivisor with a #7 lens plate). Straigh cuts can be made using dissecting scissors. They are small enough to allow you to see that you cut straight following the wires parallel to the cut.
Circular cuts might be more problematic. I would try to cut one wire at a time by slicing them with a sharp hobby knife with the mesh lying on a hard (but not too hard) surface. For example glass is way too hard and will dull the knife. I use a piece of aluminum. It is sturdy enough to support the brass wires in the mesh being cut, but soft enough not to dull a hard steel blade.
