Automatically, as in, if the mod worked with 1.84, it will have 0 problems working with 1.91. Install any mod designed for 1.84 into SE4 1.91, and it will work fine. Better, in fact, in many cases, due to improved hard coded AI behavior.
Additionally, MM made sure to keep savegames made with 1.84 compatible with the upgrade to 1.91. So, 1.84 savegames should work fine with 1.91 as well (once the PBW host processes the turn with 1.91, for PBW games).
[ February 28, 2004, 22:24: Message edited by: Imperator Fyron ]