Does ritual bathing (ghusl) become void if a person intended to bathe for a specific state of ritual impurity (janābah), then considered changing the intention to include previous states of janābah from which they had not bathed out of ignorance, but did not actually change the intention and completed their ghusl with the intention for the first janābah?

As long as you doubt the obligation of ghusl (definition), it is not obligatory for you. Your performing ghusl in this state is a continuation of whispers (waswas), which is not legislated. The cure for whispers is to ignore them and turn away from them. If you were to perform ghusl to remove a doubtful ritual impurity, your impurity would be removed according to the Shafi'is, and your ghusl would not be invalidated by what you mentioned.