Replacing Tzitzis Strings

19. If one wants to replace old tzitzis strings on his beged for nice, new ones, he does not need to untie them to avoid ruining them; he may cut them and put new ones in their place (ח"א ציצית כלל י"א סל"ב, מ"ב סי' ט"ו סק"ג ). Since it is a hassle to untie them and tzitzis strings are only worth a small amount of money, the effort to untie them is worth more than the strings themselves, and there is no issur of bal tashchis (ע”פ דרכ"מ יו"ד סי' כ"ח ).