I'm looking at this disassembly of this digital music player and radio: https://fccid.io/2AMX5-SCG110/Internal-Photos/Internal-photos-4484847

I'm unable to see a variable capacitor anywhere on the PCB. So how does it tune to different frequencies in AM?

Will it be possible to modify it to go beyond broadcast AM frequencies?

Is the ability to tune to lower and higher AM frequencies dependent on the length of the magnetic coil or variable capacitor?

 

Likely it is possible such modification, with certain limits. Example, receiving AM to 2, 3... MHz. The ability is in the chosen components to the RF chip.
Study the data sheets of mainly its receiving integrated circuits to discern what components should be tailored to reach your goal. Obtaining its schematic can also be of help.

 

Synthesized tuning

Bob

 

Google DDS (Direct Digital Synthesis), and PLL (Phase Locked Loops).