Go into the search screens and press CD.MD.CH to toggle between append and replace. An ultra-subtle + symbol will appear when in append mode.
This UI will change in the future. I was bored on the plane to Comdex and implemented the back end then just threw in a simple front end to test it.
I do not know what kind of UI change you are meaning to make on this, but if I may make a suggestion:
I rarely use the search screens, as I have my music laid out like I have it on my machine, so I know where pretty much everything is. What would be ideal for me is to append songs to a playlist by simply going through the playlist submenus, and just selecting whatever songs to append to the current playlist. (Of course, this would be a toggle, like the + in CD/MD; there would be a + somewhere whilst searching through playlists, so that you can deactivate the + and just have it work the way it does now).
Make sense? 8)
If not, I can clarify myself, I'm sure..
(O|||||O)
S/N 00246 6GB Blue