Even that theory about soft music is a bit off. I've been in my own stations several times when the national government was overthrown. On both occasions, the coup was done with the support of most of the military establishment, and immediately my offices were populated by soldiers.
They were there to make sure nothing was said on the air as all official declarations were issued by the government station (the equivalent of the BBC). There was an armed soldier in each of the 5 studios and a sergeant in the main office, with a lieutenant coming by ever hour or two.
After the second coup, when the soldiers were a bit nervous as there had been some street violence, a bit of aerial bombing and the like, I sent out for food. That went over extremely well, so a bit later, we sent out for several cases of beer. At that point the soldiers were all much more friendly and we did not fear that they might shoot us.
At no point did we have to play any music that was not part of our format.