Add additional rounds on existing SHA-512 salted hashes without knowing clear text password?

Assuming you have a salted SHA-512 password hash with 5000 rounds. For example:

{CRYPT}$  6$  rounds=5000$  6835c5dcf0bb7310$  hVod/jy7uONMSa.FVpLHb/2OrWpAj3lB/.RWdvgd3YaQAnzN3rorGhaziswwGsHfOWZYkLwXhHKnCy5By2CKr0 
  • Could one add more rounds (e.g. another 5000 rounds) to this hashed password without knowing the cleartext password such that the hash value still would be valid if a user’s cleartext password is verified?

  • If this is possible as I think it should be, are there existing tools or code to “add more rounds” to this hash value?

Btw. the cleartext password for the above hash is “password” but assume would not know this.