Question: Position Coach to Coordinator rule
I don't know the current rule, but historically the NFL has always allowed an assistant to leave his team for another job if it was a "promotion", or higher level job.
IE: assistant position coach to position coach, position coach to coordinator, etc.
Teams have gotten creative over the years - I can even recall a coordinator being allowed to leave one team to become the coordinator at another team because they were also calling him the "assistant head coach".
I believe a head coach even jumped ship once by being named head coach/general manager by the new team.
Again - I can't speak for the current status of the rules.