Preloaders are classified differently than Loader/Unloaders. Even if your building runs a pkg preload and hub sunrise sort at the same time, they generally have different managers (or FT sups if the sort is too small to necessitate a full manager). Preload to other hub shifts (TWI, Night, and Day) are equally different. It's a change in SLIC.
Talk to HR about opportunities, they can tell you the time limits and what may be available in your area. As far as the difficulty, it's all about what the manager WANTS to do.