Is it possible to “kill” a channel, or multiple channels? Like, i want to make a “drop”, or break, and i use a noise sample on a channel with gradualy rising wet slider, and also automating size to “grow”. At the end of a pattern i want to “kill” all sonund, and continue without “reverb tails” in next pattern. You could do it with rendering to sample, but is it possible to do it with some command?
It’s not possible to do it with a single command (or automation), because it’s not possible to control the post-fx volume level.
However, you can insert a Gainer device as the very last device in your DSP chain, and then automate the Gain parameter to -INF dB (ie. silence) when you want to cut the sound.
If you have a particular set of tracks that you want to apply this cut to, then you could either group them and apply the Gainer to the group, or you could use a Send Device to route them all to a send track and apply the Gainer there instead. You could also just add Gainers to each individual track and create individual automations for all of them (maximum control, but more time consuming).
As dBlue says, use a Gainer 
Still think it’s very weird Renoise allows you to automation Post Volume (Trim) but not Post Gain (Fader) as this is the exact opposite of the majority of hardware digital mixing consoles but it’s something I’ve just about got used to (Gainers re your friends, not evil incarnate.)