is not replaced by anyone.

The wording is plainly a statement of fact, so it should not be understood as a prohibition without evidence. This is the more correct interpretation.

Accordingly, what is meant is that the natural disposition upon which He created them is not replaced: they are never created without that natural disposition.

The meaning is that their original creation is not replaced such that they are created without that natural disposition. It does not mean that the natural disposition cannot change after creation. Indeed, the hadith itself makes clear that it changes. This is why he compared it to an animal born intact and subsequently mutilated. No animal is ever born castrated or mutilated.

Allah Most High said, quoting Satan:

“I will command them, and they will change Allah’s creation.”

Thus Allah, through His power and will, has enabled His creatures to change the state in which He created them.

Replacing their original creation, however, so that they are created without that natural disposition, is something only Allah can do, and Allah does not do it, as He said:

“There is no replacing Allah’s creation.”

He did not say, “There is no changing it,” for replacing something entails its passing away and something else taking its place. Thus no other creation takes the place of this creation. If, however, it is changed after coming into existence, the original constitution present at birth has not been replaced.

As for the statement, “There is no replacing the constitution of disbelief or faith with which all the children of Adam were endowed”: if what is meant is that nothing can occur contrary to what was previously decreed regarding disbelief and faith, then this is true. But this does not imply that replacing disbelief with faith, or vice versa, is impossible or beyond one’s capacity. Rather, the servant is capable of doing what Allah has commanded him