Cozumel and may other areas have the same ban. Use a pair of trauma shears. They do the job just as well and are cheaper than most knives, A z-knife is also unobjectionable and also unobtrusive. It's likewise cheap, and if you treat both with mineral oil before use, they'll last longer.
I've needed a knife on three occasions. The first two involved being snagged in fishing line, once off NJ and another time in HI, where it's common practice for fisherfolk to cut snagged line and toss it into the ocean. Grr. Probably not something you'll encounter in Egypt's protected marine parks? (speculation on my part). The third occasion was being caught in current, and using my knife in the sand to maintain position (I was observing a training dive) before making for the anchor line.