I was reading this tutorial [Only registered and activated users can see links. ]
and trying to see if I could get it to work, I can do everything up to the part about changing the "CID", that's where I'm hung up at.

I have a GPSmap 64ST and a 64X, the ST has birdseye, and I have several areas downloaded. I tried copying them to the X, after doing a hex edit on the JNX file to reflect the serial of the X instead of the ST. I entered the serial of the x unit into a decimal to hex converter, then reversed the 4 bytes, and wrote those to the JNX, but it still gives me invalid jnx.

Is there another way to do this?

Wow, I'm kind of disappointed no one knows more about this, or can at least tell me it's no longer possible.