Well, where should I begin.
Have you read the short write-up I did at our MM9 site? It's at the link below. MM9 was a sad finale to the pioneering work of 3DO. We (I) did some preliminary work on expanding on MM9 but the game never developed a strong enough fan base to justify the effort.
Our patch made the game playable, but it doesn't work on the GOG version. Gog assembled a version of the game using a different version of the game engine and some other resources. We obliquely invited them to use our work but they never even contacted us.
I need to know what you want to do. It would be a great help for today's players to adapt our 1.3 patch to work on the GOG version. That shouldn't take a lot of work and it would give you a good start understanding how the game is structured.
Graphically, Legends of Might & Magic (LOMM) and MM9 are very similar. There have been some efforts modifying LoMM to work on a later version of the Lithtech game engine. I've no idea what it would take to adapt MM9 but that might be something you're interested in looking into.
We have had previous discussions in this Tavern with folks wanting to tinker with the game. Use the 'Find' function at the top of this board to search for 'Lithtech' over the past 30,000 days. Read the full content of the threads that come up -- not just the selected posts. Think about what you want to work on and write back. It's an engaging hobby but there's a steep learning curve.