Nimbostratus
CumulonimbusThe passphrase in the SSL profile is encrypted with the device's master key for this purpose. You can export the master key to another F5 device where you intend to re-use the same SSL certificate - just make sure that that "new" device does not already have any configuration objects that was generated with that device's original master key.
Here are some resources to help you with this:
K14912: Adding and removing encryption from private SSL keys (11.x - 13.x)
K9420: Installing a UCS file containing an encrypted passphrase .