As a lone developer there is absolutely no motivation to do this and hide this decision from management.
Having said that a lone developer can come up with the idea, propose it to management with the expectation of some fat bonus. But why do this in secret?
There is just no possibility where upper management is not involved in this.
100% agree. Doing this in secret without management's express approval means no bonus, working extra for no benefit, compromising your other tasks and exposing yourself to heavy liability for compromising the country's infrastructure. This is something that companies could get away with, but a single developers would not only lose their job, but risk going to jail.
Note that management's express approval could be verbal conversations that you cannot prove happened or not. With some work management can find some way to get a developer who has some other conflict of interest to do this: if your brother in law works for the maintenance yard situations then you have motive to ensure he has work.
Having said that a lone developer can come up with the idea, propose it to management with the expectation of some fat bonus. But why do this in secret?
There is just no possibility where upper management is not involved in this.