key management – Move signing subkey to authentication slot on YubiKey (OpenPGP card)?

My PGP primary key is only used for certification—I use a separate subkey for signing. Like this:

sec  rsa4096/0x891781D0EDC66456                                                                                                                                                                                                                                                                                                
     created: 2021-09-04  expires: never       usage: C                                                                                                                                                                                                                                                                        
     trust: ultimate      validity: ultimate                                                                                                                                                                                                                                                                                   
ssb  rsa4096/0x14CF79D2D5917737                                                                                                                                                                                                                                                                                                
     created: 2021-09-04  expires: 2023-09-04  usage: S                                                                                                                                                                                                                                                                        
ssb  rsa4096/0x0041701689E0A409                                                                                                                                                                                                                                                                                                
     created: 2021-09-04  expires: 2023-09-04  usage: E                                                                                                                                                                                                                                                                        
(ultimate) (1). test user <test@example.com>                                                                                                                                                                                                                                                                                   

I noticed that the OpenPGP card spec only supports three key slots: one for signing, one for encryption, and one for authentication. There is no slot dedicated to certification. However, the keytocard command permits moving the signing subkey to the authentication slot, and moving the certification key to the signature slot.

My question: Are there any downsides to moving the keys to the card (YubiKey) as follows:

  • certification (primary) key to the signature slot
  • signing subkey to the authentication slot
  • encryption subkey to the encryption slot

In particular: Will I still be able to use the signing subkey for signing even though it’s in the authentication slot? I generated some throwaway keys and it seemed to work, but I wanted confirmation that it was OK.

The YubiKey will mostly be in cold storage, used only for the occasional certification operations (e.g., extending subkey expiration) and as a backup if I lose my main YubiKey.