giving a value to more than one ch from a unactive partition brings "error: ch list empty"

This is intended behavior. Partitions are designed to prevent unintentional control, so you can only override this for a single channel at a time. If you want to actively change multiple channels from another partition it is suggested you switch partitions to make these changes.

thanks for the answer, for what i'm doing, warning would be enough to avoid untintentional control, but i guess this protection makes sense in many cases. thanks 

just to add: i noticed that when i call a group from an inactice partition, eos reacts as for ch. and just asks me a confirm. That's the way i'll take to change multiple ch. from another partition.