Answer

Hello,
The moment the secondary legislation itself says that the authorized party has been delegated the authority to alter the law, this is possible. Beyond that, it seems to me that this is not really a change in the law but a freezing of it. For example, the Attorney General can decide not to prosecute an offense if there is no public interest in doing so—an ambiguous expression that of course receives astonishingly broad and tendentious interpretations. Even though ostensibly this runs head-on against the law, which states that for such an offense one must prosecute and punish.
The difference between positive action and passive nonperformance is because the primary legislation itself delegated authority to suspend only through passive nonperformance. And the later authorities (Acharonim) have already examined whether this is because passive nonperformance is less severe, or because uprooting a matter through passive nonperformance is not really considered uprooting. See, for example, the pamphlet of Rabbi Elchanan Wasserman regarding human dignity, which also overrides only through passive nonperformance.
I would just note that the medieval authorities (Rishonim) (such as the Raavad in Tamim De'im, and the medieval authorities on the passage in Bava Kamma that permits killing an informer) wrote in several places that in a situation of need they uproot even through positive action. The meaning of this is that the uprooting is not really uprooting but a temporary freezing for the sake of necessity. This mechanism also has sources in Maimonides, Laws of Rebels. I will discuss this in my trilogy.