Is there any way to put practise's track condition default to something else than "optimum"? Of course I can change it everytime before I start to drive but it would be much more time saving if I could set it from somewhere to "green", which I use.
In my experience the values in the driving options, including grip dynamics, stay until changed - so you don't have to adjust it everytime.
Otherwise configure a server client, you can set the exact values for the surface grip in the server_cfg.ini file. The values for the presets are written in the FAQ.