2,759. Permitting One Link in a Chain of Vows
Hilchos Nedarim 4:9
Let’s say that one person takes a vow. Another hears him and says, “Me, too.” Still another hears him and says, “Me, too.” If the first person has his vow permitted, all the others are likewise permitted. If the last person has his vow permitted, only his vow is permitted and the others are still obligated by theirs. If the second person has his vow permitted, it is permitted for him and for all those who follow him, but the first person is still obligated in his vow.
Hilchos Nedarim 4:10
The same is true when a person extends the parameters of a vow. For example, if someone took a vow prohibiting bread and he added meat to it, then having bread permitted will also permit meat, but having meat permitted will not permit bread.