When the Lord saved me at age nine, I still had a lot to learn about God, his attributes, his nature, etc.
If someone had asked me what I knew about God's immutability, I would have answered, "I don't know what that means."
I didn't deny it, I just didn't have a clue about any of that.
Now that I know what it means, what if I deny it?
The short answer is, I am still saved.
The Jesus who saved me then has kept me as he promised.
There's a difference between not knowing something and denying something. If you deny a fundamental attribute of God, you are indeed worshiping a false god.
What if you understand or interpret an attribute differently than that of another believer?
For example, two believers affirms God's omniscience, but one interprets it to mean that God knows everything that is knowable and argues that something not yet created (i.e. a free choice of man) is not knowable to God (not something I believe btw, but some do).
Does that person worship a false god because they interpret omniscience differently than you?
Keeping in mind, they affirm the Lordship and deity of of Christ and every other essential doctrine of Christianity, but only differ on this one understanding of this one divine attribute?
Can we for certain say they are worshipping a false god?
This
makes sense to me.
Another example
would be conflicting views of God's omnipotence.
One view is that God is all-powerful and even man's will is subject to His will.
Another view is that God, even in his omnipotence, has granted humans free will to accept or reject him.
The other side will say that when God gives up that kind of power to humans, his omnipotence is affected.
While we can argue, the fact is that all sides affirm God is Lord, and Jesus as deity, as you mentioned.
Both sides seek truth, just differ on what it is.