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.
If you mean what it shows in the computer while you connect it in mass storage mode and if you are using windows, right click on the drive when connected, click on properties and then edit the device name (it's an edit box up at the top, in the general tab next to the drive icon). You have to use autorun.inf to change the icon.