or what I do is just while your in piano roll, do select all [ctrl+a], then copy [ctrl+c], then go to the same channel in another pattern, open it in piano roll, hit paste [ctrl+v].... that's if you just wanna copy one channel tho, i usually dont have to edit more than a channel or two in each pattern when copying them, I try to spread out my channels through independent patterns, much easier when constructing the playlist.