Just found a pretty useful thing. I don't know, maybe i just missed it and it is well known feature.Consider you are using drums with endless sequencer, and it is running the sequence. If you switch to synth page  and start to tweak knobs, those tweakings will affect all drum sounds that currently playing in a sequence. For example, you turn blue knob (pitch) down, and while you turning it both bass drum and hihat was played, both will be pitched down. And if you press note keys, entire sequence will be pitched to corresponding key.But if you press SHIFT+key, instead of pitching it will choose certain drum sound, and moreover, it will "focus" on that sound, and now only this sound will be affected by knobs. I find it veeery handy to tweak drum sequence live, or mute some sounds on the go by turning volume of with SHIFT+RED, or similar stuff. This also works with pattern and finger sequencers, but difference is that with pattern sequencer pressing SHIFT+NOTE will both choose the sound and triggers it simultaneously, so it can be less handy to tweak sounds, but you can add some sounds over the sequence.
This tip has made me love the OP-1 even more, and I didn’t think that was even possible.