Can somebody help me to write irule to modify SSL handshake time out for a particular client?

Yes this is possible. But instead of trying to change 1 parameter for a specific source-IP, it is easier to do it this way

1. Define a new SSL profile with customized parameters lets say clientssl_slowclients.
2. Keep the virtual with the existing SSL profile.

3. In the irule, assign this SSL profile once you determine that it is a slow client.

    

   when CLIENT_ACCEPTED { if { [client_addr] ... ur checks } { SSL::profile clientssl_slowclients } }