Guys, you're right, 0 disables also in devices with integrated receiver. Garmin show up as I wrote but:
- fm_sub.bin have same size than before,
- one bit in structure is changed 1->0,

Now some info after tests:
- fm subscription info is stored in fm_sub.bin,
- before any manipulation save original file ,
- each sub appends 16 byte structure to file,
- if you add same licence with different keys structure is same,
- you can remove last added sub by removing last 16 bytes from file,
- second byte, LSB tells if sub is enabled or not,

I guess that this 16 byte structure isn't encrypted with any crypto is just bit/byte scrambled.