From the System Administrator guide:
You have the ability to regenerate the TPAM appliances’ ssh host keys. Please use with caution. Changing the appliances' ssh host key can affect CLI/API operations since the identification string for the appliance has been changed and will report an error to clients that have previously connected to the appliance. Also if you have DPAs enrolled and you regenerate the ssh host keys you must log onto the DPA console and delete TPAM from known_hosts. This is option is under the Network Settings menu, Delete TPAM from known_hosts.
In addition, SSH keys are used for asset management (logging into an asset using ssh keys stored on TPAM appliance), whereas CLI/API keys are for accessing TPAM from a remote host (logging into TPAM using ssh key stored on remote host).
The key length for SSH keys can be specified as 1024 or 2048 when generating the key. You cannot change the length of a key once it's generated. If you are currently using a 1024 bit key and wanted to change to a 2048 bit key, you would have to create a new key.
If you change an asset's SSH key in TPAM, you would have to update the appropriate authorized_keys file on the asset to ensure that TPAM could continue to login to the asset using the new key.