Foundational duties associated with the Abrahamic tradition remained in view, while broad expressions, times, and boundaries could require clarification. An obligation might be familiar in principle even when its amount, timing, conditions, or correct manner needed specification.
The foundation is the duty itself; specification may establish its timing or form; reform may remove an unauthorized addition or a corrupt custom. These are different legal operations.
Accordingly, preserving the foundation of a command is compatible with further explanation and qualification. Not every specification should be mistaken for the institution of an entirely new religious foundation.