No coding necessary. It's not without its bugs/quirks but you can use this utility to extract and compile .dir files : https://worms2d.info/WA_directory_editor
Also check out the wkTerrain thread on here for more info.

Cheers jOe, it was fun making it

New Ganja theme for use with wkTerrain: https://www.tus-wa.com/files/file-2162/

I'm not sure if this is even possible, but to get around the issue with everyone needing the same list of custom terrains installed, could wkTerrain have a command to temporarily mask all installed custom terrains apart from the one everyone agrees to play?  So for example, if all players ran something like : /Terrain Tetris, each player's game would think it only had the Tetris custom terrain installed and everyone could play?