Hi Torben,
You can't export any expansion voices from the keyboard flash memory back into YEM.
However, if you still have YEM on your old computer, then after installing YEM on the new one, you should be able to copy the data (not the program!) from the old one and paste it onto the new one.
I did this after installing YEM on a new computer without any problems. I didn't have to load any packs or content into YEM on the new PC.
The data (which includes packs, account, instruments etc) is held in a folder which, on a Windows system, is typically located at...
C:\Users\Ian\AppData\Local\YAMAHA\Expansion Manager
Obviously the actual user folder will not be 'Ian' on your system, but you should get the idea!
If you can find this on your old computer and then copy all the folders and files inside it to USB, you can then paste everything into the 'Expansion Manager' folder which should have been set up as part of installing YEM on the new machine.
This should set up YEM on your new machine just the same as it was the last time you used it on the old one. This will also ensure that any non-Yamaha packs/voices keep their existing IDs.
Note that if you have already added any packs or instruments to the new install, this procedure could overwrite the new data, so is not advised unless you know what you are doing! You could always make a back up copy of the folders/files in the 'AppData\Local\YAMAHA\Expansion Manager' folder on the new computer which you could use to restore the data if anything goes wrong!
I assume that a new version of YEM will be released anyway along with the Genos 2 firmware update expected on November 15th (to make use of the incremental update function), so you may want to wait until then, but it might be better to install the current version and its data on your new computer before this and then update to any new version from this..
Regards
Ian