I would like to be able to swap position coach duties for two coaches who are currently under contract. Currently, we need to release one, then re-sign off the open market to change.

that has been my complaint since we have to coaches in that for you to reassign coaches either be a head coach and a Offensive Coordinator , a head coach and a Defensive Coordinator , Offensive Coordinator and a position coach , a Defensive Coordinator and a position coach and/or even 2 position coaches you have to sign one to that position which fires that coach which then you have to hope no one gets that coach off the open market before you have a chance to send a contract to that coach you just fired.

me personally your idea would best way to doing it where we could reassign duties for coaching staff and even if we can only do position coaches then still it is probably way better to doing it your way than the current format.

i know that you can swap position coaches by simultaneously offering each the other's job. i am not sure if swapping can work between different coaching levels (have heard of one case where a GM said he promoted one of his position coaches to a coordinator and the coordinator 'auto-dropped down' to take over the position coach's spot (but then needed salary adjustments) but that doesn't seem to have ever happened in any of my coaching moves).

What likely happened is the coach was signed on a game stage, and because of the vacancy the AI then signed the best position coach - which happened to be the coach that was just fired.

i kind of assumed that's what happened and wasn't a 'normal' feature of human-controlled teams.