57:1 If someone said hamotzi in order to eat bread he acquired and he only planned to eat the roll or loaf he had in front of him, then he decided he wanted more and had someone go get it for him, he must recite hamotzi again on the new loaf. This is the case even if he still has some of his original bread left. This is because it’s as if he changed his mind. If, however, he has bread in the house and cuts some for himself thinking that it’s enough and then he wants to eat more, in this case he does not recite hamotzi again, even if he has completely finished his original portion. This is not like changing one’s mind, it’s just a normal way for people to eat bread.
57:2 If one said a bracha to eat some fruit and was then brought more fruit, if when he said his bracha he had in mind to include any fruit that he might be served, then the later fruit is covered by his bracha even if it is a different type of fruit and even if he has completely finished his original portion – assuming, of course, that both types of fruit take the same bracha. If, however, he only intended to eat the one fruit and he changed his mind when he was served the second, he must recite a new bracha. This is so even if the second fruit is of the same type and/or he still has some of his original fruit remaining.