I’ve also talked to certain groups of Baptists that are hard-core tulip in the second category, and it seems from what they’ve told me, they believe that if somebody prayed the prayer sincerely as a child, later decides to reject God and become an atheist, etc., God would be lying if He took away their salvation, but I am in danger of mine being taken away just because I believe that Jesus’ teachings were relevant, even though I don’t believe that following those is what saves me, just that out of love I should obey Him. (I do believe we still make mistakes as Christians and continually need God’s forgiveness).
As for predestination, my personal take is that both that and free will can be true. God knows ahead of time the decisions we’re going to make, although it does say that He calls all to repentance. Also, in the case of Pharaoh, it seems to say for the first several plagues, he hardened his own heart, and at some point, God started hardening his heart.
I think several of the conservative Mennonite churches I have attended might not have an issue with you ascribing to some TULIP theology, providing that you aren’t actively trying to convince everybody else that they are wrong. It’s not really meant to take away your right to believe what you want, just probably them wondering why you would want to be part of them if you so strongly oppose their stance on it. They would think you were trying to change them into your model of the perfect church or sheep steal.
There are some doctrines at my church that I don’t personally believe the same way they do, and they are fine with as long as I don’t actively make a big deal about arguing it (not like I’m preaching anyway