Sorry for the delay in answering, just seen this question is unanswered.
Had a look for you and found this information:
As of now, there is no direct way to rename a passkey on eBay; once you set up a passkey, you cannot change its name within the platform; you can only delete it and create a new one with a different device if you want to essentially "rename" it by associating it with a different device.
@cbucl