I’m not a philosopher, but with my “person-affecting intuitions hat” on, I think that when you bring the extra people into existence, you also bring into existence obligations for the previously existing people (i.e. if they can sacrifice a little of their wellfare for a lot of everyone else’s, they should). To count the “real” effect on their welfare, you need to factor in the obligations, and in your example the total sum comes out negatively for them (otherwise, after all the transformations, they wouldn’t be worse off, assuming that the transformations are actually realisable and the assumed moral theory actually does create obligations).
I’m not a philosopher, but with my “person-affecting intuitions hat” on, I think that when you bring the extra people into existence, you also bring into existence obligations for the previously existing people (i.e. if they can sacrifice a little of their wellfare for a lot of everyone else’s, they should). To count the “real” effect on their welfare, you need to factor in the obligations, and in your example the total sum comes out negatively for them (otherwise, after all the transformations, they wouldn’t be worse off, assuming that the transformations are actually realisable and the assumed moral theory actually does create obligations).