How many personnel/posts were you assigning, out of curiosity? I've seen a similar problem, not automated yet, with around 20 staff members, who have varying conditionals which would have to be accounted for. It's not necessarily worth my time to automate for such a small # of people, then again it's a fun puzzle.

The current approach is a 2-month rotating schedule. Since there are day/evening/overnight shifts, with overnight being the least desirable and evening the most desirable, it was deemed most equitable to simply rotate members through different 2-month schedules. This way, everyone across the year will be doing the same sets/timings of shifts in different months. This becomes very important for evening shifts, in particular, since transitioning to/from that schedule requires time to overcome the jet-lag induced.