My understanding is that the Bill of Rights was an integral part of the Constitution. Also that the Constitution itself would not be ratified without a Bill of Rights.
In other words the first 10 amendments could not be amended even if the rest of the Constitution could be changed since the Constitution itself depended on the Bill of Rights for it’s existence.
This is implied in the Pre-amble to the BoR, but an Amendment can over-ride another Amendment. See Prohibition.
Although concerned delegates to the Con-Con were assured that a bill of rights would be drafted, the articles of the Constitution were ratified before the BoR was drafted and ratified. That's why BoR is regarded as amendments to the Constitution.
Also note that James Madison, regarded as the father of both the Constitution and the Bill of Rights, was actually not supportive of a bill of rights. I understand that Madison expressed concern that, since the states never delegated to Congress the specific power to regulate our basic freedoms, that a bill of rights was unnecessary, arguably redundant.
In fact, Alexander Hamilton had essentially argued that every word amended to the Constituiton would just give unscrupuoulous lawyers another foothold to destroy the Constitution. In fact, we are now slaves to perversions of the BoR by activist justices.