Newton's Laws have not been changed. They still apply, and are used as the basis for understanding physics. The history of science is certainly filled with examples of science finding a better/more appropriate model of the universe, but the old work has rarely if ever been thrown out the window. As a general rule the new work is based upon the old, and to my knowledge the mathematics used to describe these facts have never been changed simply because the models were wrong.
What do you mean based upon? If you mean refined, or added to, you're wrong here. However if you simply mean reflected upon as new theories were developed, you're right. But this latter truth is does nothing to help an argument that Newton's Law's have a real view of the universe.
Newton's laws of gravity, and the theory behind how gravity works, were thrown away by General Relativity.
Consequently these days, General Relativity is also having trouble fitting into the Standard Model in any way other than the science interested in prediction.
Yes, it is a tool. But thinking of it as a tool implies that mathematics are a concrete set of entities which apply to the universe. And we have never had to throw these entities out.
This is not true. Mathematical concepts have been created following the logic of math that have never been used. For instance, mathematically, we can calculate a universe with 100 spacial dimensions, and a number of time dimensions, if we wanted to. This may or may not relate to reality, but it probably does not.
And I don't think "tool" was meant in a manner relating to concrete things. Just because a word implies something in some of the ways it can be used doesn't mean it was meant so. I think you know what he meant. It's sort of just forcing a person to constantly reiterate themselves. It makes arguing a droll thing, and questions how willing an arguer is to resort to artistic dodging. That might be why he didn't reply to you yet.
It is very true that the idealized triangle in one's head is simply an approximation of reality.
No, this is not very true. Have you ever heard of nominalism? Ideas and symbols in a person's head; "approximations," are debatably resembling anything objective.
I fail to see how the difference between our internal pictures of the world built through shortcuts of mathematical approximation have anything to do with whether or not mathematical entities are real.
I agree with this, but I would also agree with a culled version of this statement:
I fail to see how the difference between our internal pictures of the world have anything to do with whether or not mathematical entities are real.
In short, as I try to hint above with nominalism, there is no empirical way to identify central mathematical roles in our universe. That we can only observe matter through matter, and there is a limit to our accuracy. It seems we can only get down to a certain smallness. I'm thinking of the Uncertainly Principle here.