Little update from my side; it looks impossible for me to get an automatic "new ID to old ID" mechanism, the new ID is useless in the members area as stated before and the old ID isn't mentioned/noted anywhere on the new pages (source). Also the "update ID" as mentioned in the previews are useless in the members area.
Seems that the only option is to wait for an members area update (don't see any announcement about this atm.) where the new ID are used there also. Or someone here must have an solution that can be used in an phyton bot to get the old ID's.
So for now the service will be closed, only the packages ready to post (already downloaded) will be posted, new requests won't be noted.
Thanks.