Question:
If someone has a talis with TZIZIT but is not sure if the TZIZIT were made LISHMA or properly by G_D FEARING JEWS or whatever one wants like puting on better TZIZIT or MENUPETZ or thicker? The TZIZIT are perfectly new. CAn one cut (with plastic or glass) the TZIZIT and put on new TZIZIT LISMA ? Would it be better to untie them? CAN THIS EVEN BE DONE?Are you shaming the TALIS or the MITZVAH?
Answer:
What you are writing is true, there is an idea of not untying tzitzis for no reason because it is shaming the tallis, (see Shulchan Aruch O:CH 15-1). The M:B (15-3) says there that if the person wants to change the tzitzis for (physically of halachically) nicer ones, that it is permitted to remove them in order to change them for the better ones. It is better to untie them, instead of cutting them, because then they can be used by someone else, however if this is difficult, it is permitted to cut them also.
Best wishes
