A more moderate take from a cop:

Most agencies are going to insist officers continue to knock and announce, if for no other reasons than officer safety and to avoid the obvious lawsuit by a homeowner getting shot while defending himself during what he may think is a home invasion.
As a law enforcement officer myself I intend to knock and yell “police” at the top of my lungs like always. It is bad enough to get shot at by the bad guys, much less a half-asleep or startled good guy.