There currently is no way to merge multiple tracks into a single GPX file without actually merging them into one track. You'd have to select them all, and then cut them later.
How about if you select the files you want in the active list, and then right click to choose "save merge as..." ? That seems like the best way to add it to me.
You can reverse tracks. Just select one with the merge/profile tool and then hit the 'v' key, or, with the track selected, right click somewhere on the map to get a menu with a "reverse" option. If you're merging multiple tracks it'll only reverse the last one added.
Hope this helps.