I would advise against it especially if you plan on applying it directly to the material while it is still on the helmet as it will leach. You would look the height of village if during a long innings it begins to drip off the helmet and on to your face with the heat. I would suggest-and I have seen this done- removing the fabric intact and then using its dimensions as a template from which to cut new cloth. You can do it yourself with a little practice or pay a tailor to do it for you. I do not envisage it would cost too much to do.