I've had good success with this, this morning.
Took a book (.mobi) and added ASIN number (taken from amazon) and EBOK tags to the metadata with mobi2mobi.
Added it manually to my android kindle folder.
Added it manually to my kindle via windows explorer.
Opened both and played around, each device asked could it sync to the latest location from the other device. Perfect.
Then removed book from kindle and transfered it via calibre to see if it kept the metadata during the transfer.
It did. Opened new book in kindle and clicked the sync to furthest location. Went directly to where I was in the android version. Nice.
I have not tested converting a book INSIDE calibre after adding the asin data to see if it maintains the ASIN data, as I don't think this is something that is like to happen to *me*.
I didn't experience any book cover issues at the moment on the android but that may be because I used the corretc ASIN number and not a dummy number...
Finding a plugin for calibre to bulk import the asin number from amazon would be lovely. I cannot help in this department sorry!
Hope that might help someone.