You do have the option to move or change icons in the drawer. Go to settings, change view to grid. Go to right where there is empty space. Press icon you want to move (ie message because I use Hancent), press till it wiggles, then drag to empty space.
Scroll over to whatever you want to drag down, wiggling, and drag and drop to empty space. Hit home to end.
Any and all apps can be replaced, but stil limited (I believe) to 4 in drawer.