... but it irks me when heritage stations flip formats with little or no warning.
It might help to understand the business side of format flips.
Going back a number of decades, it was very common to find situations where a the playbook for the flip was to have the new staff at a nearby motel along with carts of all the music and jingles and a book full of liners. The current format would end with the mass firing of the old format staff. The idea was to keep the change a total secret from the competition so that they could not react to counter the change.
Another reason for not advising of a format change is internal. Announcers who know their job will be over tend to engage in negative behaviour, ranging from swan songs to outright sabotage. I know of one case where, before leaving, a terminated jock peed in the production room board, ruining it totally. As to swan songs, when the operator I was with bought a rock station to convert it to Spanish language, the hard rock jocks spent a several months making negative remarks about Latin music, Hispanics and the changes in Los Angeles demographics.
So there are plenty of reasons not to let anyone know about a change and essentially no reasons to publicize it.