FM Radio changing frequencies

Possible? Yes.

Easily? That TOTALLY depends on the specific radio you're going to try to do it to. Some models, it'll be as easy as carefully tweaking a coil or fiddling with the tuning capacitor. Other models might require an almost complete-from-scratch redesign.

Basically, you have to move the tuning range from the broadcast FM band to whatever frequency your "target" uses. Doing that might be easy, or it might be complex, or it might even be impossible, depending on your radio's exact circuit details.

There's simply no way to tell in advance without having detailed circuit information on the exact radio you're going to try doing it to.

I have done it for my FM radio in the past, when we still had NON-encoded police radio just below the FM band. The problem was that the FM modulation depth was only 15 KHZ instead of the 250 KHZ used by commercial FM stations, so the sound was very soft and when turned up, the noise level in between transmissions was horrible. Today we only have encoded police/ambulance/emergency services.

A BFO might avoid the need to disturb the radio's internal adjustments.