suppose i am a military aircraft and i go 'quad 0' or 'quad 7' on the transponder, is there some way to stop ATC to asking me to retune to the previous channel? perhaps some kind of command to cancel flight following or the flight plan or what ever else might be in effect, before the ATC issues a verbal Que?

No, there is not.

Only if you are flying on VATSIM :), and even then they may harass ya.

did not think so, i guess the political climate is not right for stuff like squaking 7500 in flightsim_X. though they ought to read and respond to 7600 and 7700.