Performances are assigned the category that is in Part 1 of the performance. If you want your performance to be No Assign you will need to have an Init part in Part 1. You could use this as a way of grouping your own performances together to make them easier to search for (you would need to mute part 1 if it's only for this purpose).

Thanks Phil but part are more precious than category. I don't like to see my program when I search in the category search.
I suggest that in next firmware user category will be added or possibility to give no property to a user program.

You could still use part 1 as a sound by copying the elements of another part to the elements of part 1 - it will still have its Init designation as that was how it was originated.