If he removed the tallit gadol in order to enter the toilet room or for some other business with the intention of putting it back on immediately, he need not say the blessing over it again. Even though Maran z"l reasons that one should recite it, we maintain "safek berakhot lehakel/if in doubt, do not recite a berakhah," and even against the reasoning of Maran z"l. This too is the rule with the tallit katan if he removed in to go in to immerse [in a mikvah], he should not say a berakhah when he dons it when he goes out, due to safek berakhot lehakel, and even though it is explicitly stated in Sefer Hakavanot of Rabeinu the Arizal that his practice was to say the berakhah on the tallit katan after immersion, and we do not say that safek berakhot takes precedence over Rabeinu the Arizal, anyhow it could be said that Rabeinu the Arizal is different, because he would linger in the immersion and do many kavanot, so that some hesech daat/diversion of mind is made. However if he removes it in order to enter the bath where he will stay long, it is preferable to say the berakhah as the Arizal did. This is what I brought up in my holy book Mekabtziel. But if he changes his clothes and dons a different tallit katan, even if he dons it immediately after removing the first one, he should say the berakhah on the new one, an this too is the rule with a tallit gadol if he removes the one that is on him and dons a different tallit gadol, he should say the berakhah on the second one. And in my holy book Rav Pealim I wrote a responsa bs"d, regarding someone whose practice it is to don tzitzit and tefilin each day in his house, in order to enter the synagogue in tzitzit and tefilin, but because he walks in pathways where many people pass back and forth, those of the Brit and those who are not of the Brit, he does not don the tallit gadol that he has in the synagogue, because it is visible to people, but instead he has a very thin tallit that large enough to be a tallit gadol but is not very big, and he dons in his house under his coat, and because it is very fine and also because it is not long it is not visible to people who apss by, and when he enters the synagogue he leaves this one on him under his coat, and dons the tallit gadol that he has, and I brought up bs"d that he can say the berakhah in the synagogue on the second tallit, even though the first one is on him that he said a blessing over in his house, because there is a gap between [going from] his house to the synagogue, and also there is a hesech daat since he says verses by the mezuzah, and furthermore it takes him much time to walk the path, and there in the synagogue he dons a different tallit that is full-sized, wrapping his head and body, while the tallit that is on him rests on his shoulder and legs, and also I found other reasons regarding this why he should say the berakhah, so one should not have any doubt on this regarding safek berakhot.