You set a custom name (afair in bt settings) which changes only bt name and internal device name for file manager.
That is a N900 system setting. And is still correct, right?

So you want the device name shown on your PC to be changed, did I understand correct?
As you formatted the eMMC, your PC recognizes this as a "new" SD/USB/removable device. Just right-click (or F2) and change in Windows Explorer, according to your wishes.