This loosens its adhesion to the substrate and makes the caulk easier to cut with a knife. Press the knife all the way into the brownies with steady pressure.

High Temperature Resistant Silicone Polyimide Film Die Cut Adhesive Tape
How to cut silicone cleanly. Lay the mat flat on the ground. Follow these simple steps for a safe clean and straight cut. Then using the straight edge mark the line where you will cut with your chalk. Open the caulk tube by cutting the tip of the nozzle at a 45 degree angle using a utility knife then insert a long clean nail or wire into the nozzle to puncture the inner seal. Place the tape measure on one end of the hose and mark at the desired length. Poke through the seal a few times to ensure a smooth flow of caulk.
Repeat until the brownies are cut into 2 in 51 cm strips. If you having difficulty making clean cuts try wiping your blade on a paper towel after each cut. Pull the blade downwards to cut through the piping halfway. Cut slowly to ensure a clean line. You can simply use the blade that is found on the inside of the caulking gun to cut off the tip of the tube. A quick look at how you can get clean lines when you need to caulk a seam.
All the silicone i have worked with will cut easily with a sharp knife. Do this several times until the line is visible and straight. To remove stubborn caulk you can either apply the solvent repeatedly or soak a rag and place the rag on the caulk. Hold the knife perpendicular to the piping and insert the tip of the blade into the middle. Cutting out the bulk solvents such as vinegar or mineral spirits and even stronger ones like lacquer thinner swell cured silicone caulk. Many people use knives or scissors but there is a much better way.
Cut your brownies vertically at each of the marks you made. Pull the knife around to the other uncut side of the piping and slowly cut though the rest of the piping. Now place your straight edge on the cutting mark firmly and use your sharp utility knife to score the line two to four times. A permanent marker works well for this and will clean right off with a little bit of alcohol once you are done. It will allow you to. But tex is right.
You just need a very sharp blade such as an x acto knife or a utility knife with a new blade in it.