In general i do not use default ATC, however i tune to active frequencies just to hear ATC communication.

That greatly improves atmosphere and feeling of being there.

I was thinking if that is possible to update FS2Crew in such way that as option FO will always tune to P3D default ATC active frequency ?

That would certainly be a very nice option as I do the same with default ATC. Even if you use it to actively control your aircraft it would be nice if the FO handled the communication and or frequency changes.

It's a good idea, but controlling the default ATC is very tricky.  It tried it in the FS Labs Airbus version to get clearances, and it's icky.

The FS SDK's just don't provide that much control over the ATC system.