There was no change of mind. That's merely your straw man. Your 2nd question is invalid, because the world is not excluded. The people excluded are those who persist in unbelief until the end. IOW, the "many called" which are not the "few chosen."
It is error to pit scripture against scripture which you seem to be doing, that is, Jn 3:16 against Jn. 17:9. In Jn. 17:9 is it not obvious that those He is praying for are only the elect, who "will believe on account of their word"? If He says "I am not praying for the world", does this mean He is not praying for every person without exception? But the context demands that we understand "the world" in this sense has a scope, and that scope is all who will not ever believe in Him. Do you agree?
So Jn. 3:16 also has a context, and it is erroneous to assume anything about it without examining the context. It is also erroneous to assume something about it that is in conflict with other scripture. So interpretation is important in understanding the meaning. Would you agree that given Jn. 17:6 that the love of God is greater for believers than for unbelievers? Doesn't natural love tell us that love is not a switch either on or off, that it has degrees?
If we say that the context of Jn. 3:16 is the "whole world," then does this not imply that God's love is in greater degree for those who believe in Christ than those who perish? We cannot exclude the wider context of scripture in which God declares that He hates certain people who exhibit wickedness, malice, etc. So then, "the world" in the context of Jn. 3:16 must mean that God loves the whole world in a generic sense, so that He is not talking about every individual. The greater love goes toward those who believe, because they are given eternal life. But 3:36 says, "he who believes has eternal life, but he who does not believe will not see life, but the wrath of God abides on him." Therefore, if anyone hears Jn. 3:16 and hopes that he is one of those whom God loves (because he is part of the world), then that person has the opportunity to be reconciled to God and obtain eternal life. But whoever disregards Jn. 3:16, that person does not have any opportunity. I think we could agree on that, couldn't we?