Hi Karl,
If you first create a new pack in YEM (or select an existing one), you can then actually import UVN/UVD files directly into it as content in recent versions of YEM, removing the need for a UVI Library file.
The advantage of using a UVI is that creating a pack using it will ensure that the UVNs are assigned the same Program Change numbers in the new pack as they were in the UVI, but you can change these numbers after import, so it is not a big problem.
Of course, to change them to correctly match the T4 setup, you would need to know the 'slot' in the Custom Voice Table in which each voice was installed in the Tyros4. You would also need to know this even if you wanted to recreate a UVI and use this to create the pack!
The Program Change number is only really an issue if you have registrations from the T4 which use these custom voices which you want to transfer to Genos.
Regards
Ian