Playing songs that are within the old format is rather subtle. I've never seen a format or ownership/format change where there was control put on the playlist. But I know many cases going back decades where the things said by the airstaff are controlled.
The most common thing the seller does is reduce severance pay in proportion to the negative remarks. In one case, for every negative remark (and they named a respected local authority as arbitrator) one week of severance would be deducted. That worked well, and the transition was seamless.
Don't most format flips happen without notice. The jocks usually don't get a 3 day grace period before a flip or sale. Either the sale happens at midnight and the jocks are out the next day. Or the format flips and everyone gets fired.