Can I cut my tzitzis as the strings are very very long as long as I keep them to the required length?
We are allowed to cut the tzitzis strings if they are too long or if in order that they should all be the same length, as long as they are not cut shorter than the required length. The tzitzis should preferably not be cut with metal, (scissors, knife or razor) and if possible it is better with the person’s teeth. The reason not to cut them with metal is similar to the idea of not cutting the mizbeach with metal. Since the mizbeach’s purpose is to lengthen a person’s life and metal shortens it, therefore we don’t cut the mizbeach with metal. In a similar way tzitzis lengthen a person’s life.
O:CH 11-4, Rema ibid, M:B ibid 61, Kaf Hachaym Ibid 17, Shulchan Aruch Horav 11-24, PIskei Teshuvos 11-29. The reason to specifically cut them with ones teeth (if possible) is because a person has 32 teeth, and it is a segulah not to get tooth aches. See Magen Avrohom 11-18 from the Shelah, and Mateh Moshe, also see Machtzis Hashekel.