Changing teams no longer crashes servers. In addition, the Modular Combat dedicated server package is now finally working (it wasn't Valve's fault after all)! The short answer is for game server operators to install package 366360. The long answer is in the Dedicated Server guide.
Valve recently added a "Community-Made Mod" program to Steam and as a result Modular Combat now requires players to own Half-Life 2. It's unknown if this affects players who already downloaded Modular Combat but don't have HL2, but it definitely affects new players who don't own HL2. It's highly unlikely we can get this requirement removed.
For the past week I've been working on a huge new map for Modular Combat. I don't want to over-hype, so I'll just sum it up in one short sentence: it has a maze you can explore that randomizes its layout every round. I don't know when it will be done, but im around 60% finished.