Mike,
Don't take this as gospel, but since Mica is apparently out for a few days, here are a few thoughts that might help.
- Since you're going from heavier to lighter strings, you shouldn't have to do anything with the tailpiece. The slots here might be wider than needed for the thinner strings, but it won't make any difference in sound.
- You'll need a new nut (probably just the top piece), and at least new bridge saddles, both to have smaller slots.
- If you can handle the slotting yourself, or have someone local who will do it for you, you can probably get away with a nut blank and a set of bridge saddles. Then it would be just a matter of filing slots to match the gauges of the new strings.
- If you are thinking about switching back and forth, then you might decide to spend the money for a complete second bridge, because disassembling to replace all the saddles, re-adjusting intonation, etc. would be a bit of a nuisance. But if you just want to try it for a while, a set of saddles alone would certainly be less expensive.
- If you want everything done for you by Alembic, you'll probably need to provide more detailed measurements of your existing hardware (in addition to the string gauges you intend to use). After all, these are handcrafted instruments, and even something as relatively simple as a nut may not always be interchangeable.