Do not "jar" the audience. This is the first point I want to make on this subject. People listen to music on the radio for different reasons mostly for the music. There are a few country radio stations down here in Delaware that feature country music. Some stations, play contemporary country, one station features country music that sounds like country--so Florida Georgia Line would not be heard on this station but Tim McGraw, Brad Paisley or George Strait would. There is also a classic country station that plays only the classics. The audience can pick and choose the country station that appeals to them.
Edgewater Gold Radio plays oldies. Our audience knows that they will hear a large variety old oldies from the 50s through the 80s. Variety is key and that's what we stress. Within our format, we feature a 60s and 70s oldies weekend. We are not jarring the audience but are appealing to those listeners who love hearing the 60s and 70s.
Our disco show was our biggest risk. On Saturday night, we play classic disco from 7pm to 12 mid. Now lots of people don't like disco. We try to appeal to the audience that loved the era from the mid 70s to early 80s. Even though the songs are disco, they are still oldies. We strongly promote the show and make sure that the audience is aware that at 7pm on Saturday night we will switch to disco. There can be variations within the format but you must tell your audience what you're doing.
Some stations will play all sorts of music. I heard Bobby Sherman's "Julie Do You Love Me" on a station that plays pop 80s as their main format. This jarred me! I play Bobby Sherman but Edgewater Gold Radio is an oldies station so you would expect to hear it there. Jarring turns the audience off---Keep your format consistent. Don't try to be everything to everyone!