In case you need to switch between various OSes (be it Windows and Linux, or just various Linux distros).
/var/lib/bluetooth/[MAC address of Bluetooth]/linkkeys
you can as well just copy whole
Inside the registry:
Note that to read it you need to run regedit this way:
psexec -s -i regedit.exe
And for that you need to download PsExec from sysinternals.
More details at this stackexchange answer.